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	$55.51	7.350%	$59.59	$59.59	$59.60	$59.60
Purchase #2	$96.46	8.589%	$104.7449	$104.74	$104.75	$104.70
Purchase #3	$15.45	11.814%	$17.2753	$17.28	$17.30	$17.30
Purchase #4	$50.41	6.843%	$53.8596	$53.86	$53.85	$53.90
Purchase #5	$41.36	10.487%	$45.6974	$45.70	$45.70	$45.70
Purchase #6	$71.36	8.482%	$77.4128	$77.41	$77.40	$77.40
Purchase #7	$232.77	6.345%	$247.5393	$247.54	$247.55	$247.50
7 purchase totals =	$563.32		$606.1193	$606.12	$606.15	$606.10