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	$226.33	13.609%	$257.1312	$257.13	$257.15	$257.10
Purchase #2	$113.53	13.469%	$128.8214	$128.82	$128.80	$128.80
Purchase #3	$129.42	13.281%	$146.6083	$146.61	$146.60	$146.60
Purchase #4	$196.77	6.465%	$209.4912	$209.49	$209.50	$209.50
Purchase #5	$108.59	7.639%	$116.8852	$116.89	$116.90	$116.90
Purchase #6	$70.29	11.225%	$78.1801	$78.18	$78.20	$78.20
Purchase #7	$248.47	10.486%	$274.5246	$274.52	$274.50	$274.50
7 purchase totals =	$1,093.40		$1,211.6420	$1,211.64	$1,211.65	$1,211.60