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	$245.95	10.314%	$271.3173	$271.32	$271.30	$271.30
Purchase #2	$67.89	3.363%	$70.1731	$70.17	$70.15	$70.20
Purchase #3	$33.69	3.735%	$34.9483	$34.95	$34.95	$34.90
Purchase #4	$209.42	4.653%	$219.1643	$219.16	$219.15	$219.20
Purchase #5	$90.52	10.240%	$99.7892	$99.79	$99.80	$99.80
Purchase #6	$225.96	13.167%	$255.7122	$255.71	$255.70	$255.70
Purchase #7	$121.39	13.178%	$137.3868	$137.39	$137.40	$137.40
7 purchase totals =	$994.82		$1,088.4912	$1,088.49	$1,088.45	$1,088.50