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	$36.25	12.109%	$40.6395	$40.64	$40.65	$40.60
Purchase #2	$196.26	5.666%	$207.3801	$207.38	$207.40	$207.40
Purchase #3	$39.51	10.832%	$43.7897	$43.79	$43.80	$43.80
Purchase #4	$43.60	13.485%	$49.4795	$49.48	$49.50	$49.50
Purchase #5	$209.68	5.639%	$221.5039	$221.50	$221.50	$221.50
Purchase #6	$230.46	11.462%	$256.8753	$256.88	$256.90	$256.90
Purchase #7	$76.42	9.404%	$83.6065	$83.61	$83.60	$83.60
7 purchase totals =	$832.18		$903.2745	$903.28	$903.35	$903.30