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	$81.87	10.776%	$90.6923	$90.69	$90.70	$90.70
Purchase #2	$234.43	7.137%	$251.1613	$251.16	$251.15	$251.20
Purchase #3	$213.70	13.797%	$243.1842	$243.18	$243.20	$243.20
Purchase #4	$204.42	5.812%	$216.3009	$216.30	$216.30	$216.30
Purchase #5	$94.67	10.179%	$104.3065	$104.31	$104.30	$104.30
Purchase #6	$13.32	10.287%	$14.6902	$14.69	$14.70	$14.70
Purchase #7	$243.39	13.375%	$275.9434	$275.94	$275.95	$275.90
7 purchase totals =	$1,085.80		$1,196.2788	$1,196.27	$1,196.30	$1,196.30