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	$48.34	10.408%	$53.3712	$53.37	$53.35	$53.40
Purchase #2	$54.68	6.482%	$58.2244	$58.22	$58.20	$58.20
Purchase #3	$56.57	8.583%	$61.4254	$61.43	$61.45	$61.40
Purchase #4	$146.46	8.868%	$159.4481	$159.45	$159.45	$159.40
Purchase #5	$180.60	8.797%	$196.4874	$196.49	$196.50	$196.50
Purchase #6	$5.46	7.166%	$5.8513	$5.85	$5.85	$5.90
Purchase #7	$40.37	12.344%	$45.3533	$45.35	$45.35	$45.40
7 purchase totals =	$532.48		$580.1611	$580.16	$580.15	$580.20