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	$88.28	13.196%	$99.9294	$99.93	$99.95	$99.90
Purchase #2	$54.95	12.357%	$61.7402	$61.74	$61.75	$61.70
Purchase #3	$98.73	6.121%	$104.7733	$104.77	$104.75	$104.80
Purchase #4	$54.80	6.847%	$58.5522	$58.55	$58.55	$58.60
Purchase #5	$26.46	9.331%	$28.929	$28.93	$28.95	$28.90
Purchase #6	$55.41	11.821%	$61.96	$61.96	$61.95	$62.00
Purchase #7	$146.26	5.517%	$154.3292	$154.33	$154.35	$154.30
7 purchase totals =	$524.89		$570.2133	$570.21	$570.25	$570.20