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	$247.31	9.688%	$271.2694	$271.27	$271.25	$271.30
Purchase #2	$74.27	6.106%	$78.8049	$78.80	$78.80	$78.80
Purchase #3	$108.41	4.738%	$113.5465	$113.55	$113.55	$113.50
Purchase #4	$117.61	3.688%	$121.9475	$121.95	$121.95	$121.90
Purchase #5	$184.81	13.503%	$209.7649	$209.76	$209.75	$209.80
Purchase #6	$152.35	9.341%	$166.581	$166.58	$166.60	$166.60
Purchase #7	$36.84	10.272%	$40.6242	$40.62	$40.60	$40.60
7 purchase totals =	$921.60		$1,002.5384	$1,002.53	$1,002.50	$1,002.50