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	$47.53	12.573%	$53.5059	$53.51	$53.50	$53.50
Purchase #2	$88.94	5.696%	$94.006	$94.01	$94.00	$94.00
Purchase #3	$132.83	11.549%	$148.1705	$148.17	$148.15	$148.20
Purchase #4	$45.45	4.516%	$47.5025	$47.50	$47.50	$47.50
Purchase #5	$59.35	3.196%	$61.2468	$61.25	$61.25	$61.20
Purchase #6	$55.42	5.727%	$58.5939	$58.59	$58.60	$58.60
Purchase #7	$47.39	6.111%	$50.286	$50.29	$50.30	$50.30
7 purchase totals =	$476.91		$513.3116	$513.32	$513.30	$513.30