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	$71.32	5.839%	$75.4844	$75.48	$75.50	$75.50
Purchase #2	$57.69	8.539%	$62.6161	$62.62	$62.60	$62.60
Purchase #3	$140.70	12.780%	$158.6815	$158.68	$158.70	$158.70
Purchase #4	$69.64	4.557%	$72.8135	$72.81	$72.80	$72.80
Purchase #5	$58.39	12.684%	$65.7962	$65.80	$65.80	$65.80
Purchase #6	$52.62	13.309%	$59.6232	$59.62	$59.60	$59.60
Purchase #7	$242.25	13.583%	$275.1548	$275.15	$275.15	$275.20
7 purchase totals =	$692.61		$770.1697	$770.16	$770.15	$770.20