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	$83.39	7.297%	$89.475	$89.48	$89.50	$89.50
Purchase #2	$224.27	11.605%	$250.2965	$250.30	$250.30	$250.30
Purchase #3	$13.56	8.541%	$14.7182	$14.72	$14.70	$14.70
Purchase #4	$133.29	13.670%	$151.5107	$151.51	$151.50	$151.50
Purchase #5	$147.90	12.353%	$166.1701	$166.17	$166.15	$166.20
Purchase #6	$134.35	11.532%	$149.8432	$149.84	$149.85	$149.80
Purchase #7	$135.86	9.523%	$148.7979	$148.80	$148.80	$148.80
7 purchase totals =	$872.62		$970.8116	$970.82	$970.80	$970.80