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	$56.96	3.151%	$58.7548	$58.75	$58.75	$58.80
Purchase #2	$48.97	9.580%	$53.6613	$53.66	$53.65	$53.70
Purchase #3	$124.29	9.623%	$136.2504	$136.25	$136.25	$136.30
Purchase #4	$75.98	3.151%	$78.3741	$78.37	$78.35	$78.40
Purchase #5	$70.89	10.748%	$78.5093	$78.51	$78.50	$78.50
Purchase #6	$125.53	8.836%	$136.6218	$136.62	$136.60	$136.60
Purchase #7	$250.50	13.855%	$285.2068	$285.21	$285.20	$285.20
7 purchase totals =	$753.12		$827.3785	$827.37	$827.30	$827.50