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	$27.61	11.213%	$30.7059	$30.71	$30.70	$30.70
Purchase #2	$70.77	10.418%	$78.1428	$78.14	$78.15	$78.10
Purchase #3	$160.47	3.746%	$166.4812	$166.48	$166.50	$166.50
Purchase #4	$64.44	7.607%	$69.342	$69.34	$69.35	$69.30
Purchase #5	$100.51	4.437%	$104.9696	$104.97	$104.95	$105.00
Purchase #6	$61.74	6.398%	$65.6901	$65.69	$65.70	$65.70
Purchase #7	$139.28	8.625%	$151.2929	$151.29	$151.30	$151.30
7 purchase totals =	$624.82		$666.6245	$666.62	$666.65	$666.60