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	$53.53	7.727%	$57.6663	$57.67	$57.65	$57.70
Purchase #2	$176.66	8.360%	$191.4288	$191.43	$191.45	$191.40
Purchase #3	$172.88	11.307%	$192.4275	$192.43	$192.45	$192.40
Purchase #4	$103.58	9.392%	$113.3082	$113.31	$113.30	$113.30
Purchase #5	$75.29	10.468%	$83.1714	$83.17	$83.15	$83.20
Purchase #6	$28.37	4.760%	$29.7204	$29.72	$29.70	$29.70
Purchase #7	$155.89	6.741%	$166.3985	$166.40	$166.40	$166.40
7 purchase totals =	$766.20		$834.1211	$834.13	$834.10	$834.10