Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$33.89	5.788%	$35.8516	$35.85	$35.85	$35.90
Purchase #2	$155.50	10.227%	$171.403	$171.40	$171.40	$171.40
Purchase #3	$127.98	10.743%	$141.7289	$141.73	$141.75	$141.70
Purchase #4	$108.67	12.681%	$122.4504	$122.45	$122.45	$122.50
Purchase #5	$132.66	13.636%	$150.7495	$150.75	$150.75	$150.70
Purchase #6	$43.29	4.202%	$45.109	$45.11	$45.10	$45.10
Purchase #7	$78.91	5.473%	$83.2287	$83.23	$83.25	$83.20
7 purchase totals =	$680.90		$750.5211	$750.52	$750.55	$750.50