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	$79.74	11.755%	$89.1134	$89.11	$89.10	$89.10
Purchase #2	$62.98	11.261%	$70.0722	$70.07	$70.05	$70.10
Purchase #3	$228.55	5.635%	$241.4288	$241.43	$241.45	$241.40
Purchase #4	$165.55	4.771%	$173.4484	$173.45	$173.45	$173.40
Purchase #5	$152.67	4.318%	$159.2623	$159.26	$159.25	$159.30
Purchase #6	$188.27	8.781%	$204.802	$204.80	$204.80	$204.80
Purchase #7	$113.87	8.200%	$123.2073	$123.21	$123.20	$123.20
7 purchase totals =	$991.63		$1,061.3344	$1,061.33	$1,061.30	$1,061.30