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	$133.51	9.754%	$146.5326	$146.53	$146.55	$146.50
Purchase #2	$66.56	8.408%	$72.1564	$72.16	$72.15	$72.20
Purchase #3	$220.77	9.232%	$241.1515	$241.15	$241.15	$241.20
Purchase #4	$77.71	11.332%	$86.5161	$86.52	$86.50	$86.50
Purchase #5	$86.77	13.449%	$98.4397	$98.44	$98.45	$98.40
Purchase #6	$149.70	4.145%	$155.9051	$155.91	$155.90	$155.90
Purchase #7	$175.25	7.715%	$188.7705	$188.77	$188.75	$188.80
7 purchase totals =	$910.27		$989.4719	$989.48	$989.45	$989.50