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	$52.33	10.662%	$57.9094	$57.91	$57.90	$57.90
Purchase #2	$216.71	7.839%	$233.6979	$233.70	$233.70	$233.70
Purchase #3	$32.97	13.829%	$37.5294	$37.53	$37.55	$37.50
Purchase #4	$171.65	7.579%	$184.6594	$184.66	$184.65	$184.70
Purchase #5	$146.40	13.680%	$166.4275	$166.43	$166.45	$166.40
Purchase #6	$16.56	11.783%	$18.5113	$18.51	$18.50	$18.50
Purchase #7	$207.55	7.428%	$222.9668	$222.97	$222.95	$223.00
7 purchase totals =	$844.17		$921.7017	$921.71	$921.70	$921.70