The manual for the Canon P1-DHV is online at http://www.usa.canon.com/app/pdf/calculator/P1-DHV_G_USA_HWB.pdf>.
When the display shows "5/4", the calculator is doing 5/4 rounding which means: 5 or above round up, 4 or below round down. To control rounding press the "5/4" key.
When the display shows "E" the calculator could not complete a calculation. It can be because of dividing by 0, or because the total exceeded 1 trillion, or because the operator entered calculations faster than the calculator could complete them. Press the CI/C key to clear it.
I can't explain why you are not getting a total on the tape. Try the following example from the manual exactly as shown, and let me know if your tape shows the total.
- Clear the calculator (press [CI/C])
- Choose 5/4 rounding (press [5/4] until "5/4" displays)
- Choose add mode (press [DEC] until "A" displays)
- Choose cost-sell-margin mode (press [B-T] until "B" displays)
- Turn printer on (press [PRINT] until "PRINT" displays)
- To calculate: $12.55 + $15.75 - $5.30
- Key in: 1255 [+] 1575 [-] 530 [=]
- Tape shows: [0. C] ... [12.55 +] ... [15.75 -] ... [5.30 =] ... [23.00 *]