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	$55.91	5.113%	$58.7687	$58.77	$58.75	$58.80
Purchase #2	$99.64	6.284%	$105.9014	$105.90	$105.90	$105.90
Purchase #3	$65.42	10.358%	$72.1962	$72.20	$72.20	$72.20
Purchase #4	$57.60	6.720%	$61.4707	$61.47	$61.45	$61.50
Purchase #5	$106.43	4.454%	$111.1704	$111.17	$111.15	$111.20
Purchase #6	$203.69	10.538%	$225.1549	$225.15	$225.15	$225.20
Purchase #7	$30.32	13.309%	$34.3553	$34.36	$34.35	$34.40
7 purchase totals =	$619.01		$669.0176	$669.02	$668.95	$669.20