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	$230.90	10.627%	$255.4377	$255.44	$255.45	$255.40
Purchase #2	$148.50	7.403%	$159.4935	$159.49	$159.50	$159.50
Purchase #3	$104.34	11.607%	$116.4507	$116.45	$116.45	$116.50
Purchase #4	$20.35	9.574%	$22.2983	$22.30	$22.30	$22.30
Purchase #5	$117.40	9.771%	$128.8712	$128.87	$128.85	$128.90
Purchase #6	$233.67	9.824%	$256.6257	$256.63	$256.65	$256.60
Purchase #7	$120.53	9.606%	$132.1081	$132.11	$132.10	$132.10
7 purchase totals =	$975.69		$1,071.2852	$1,071.29	$1,071.30	$1,071.30