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	$89.86	11.614%	$100.2963	$100.30	$100.30	$100.30
Purchase #2	$23.84	3.328%	$24.6334	$24.63	$24.65	$24.60
Purchase #3	$118.96	8.547%	$129.1275	$129.13	$129.15	$129.10
Purchase #4	$209.45	6.333%	$222.7145	$222.71	$222.70	$222.70
Purchase #5	$134.43	13.766%	$152.9356	$152.94	$152.95	$152.90
Purchase #6	$230.57	9.414%	$252.2759	$252.28	$252.30	$252.30
Purchase #7	$237.48	13.634%	$269.858	$269.86	$269.85	$269.90
7 purchase totals =	$1,044.59		$1,151.8412	$1,151.85	$1,151.90	$1,151.80