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	$67.73	3.834%	$70.3268	$70.33	$70.35	$70.30
Purchase #2	$108.61	7.869%	$117.1565	$117.16	$117.15	$117.20
Purchase #3	$59.94	11.168%	$66.6341	$66.63	$66.65	$66.60
Purchase #4	$12.52	8.775%	$13.6186	$13.62	$13.60	$13.60
Purchase #5	$94.59	11.304%	$105.2825	$105.28	$105.30	$105.30
Purchase #6	$60.72	7.485%	$65.2649	$65.26	$65.25	$65.30
Purchase #7	$85.39	8.837%	$92.9359	$92.94	$92.95	$92.90
7 purchase totals =	$489.50		$531.2193	$531.22	$531.25	$531.20