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	$16.96	9.569%	$18.5829	$18.58	$18.60	$18.60
Purchase #2	$249.75	7.111%	$267.5097	$267.51	$267.50	$267.50
Purchase #3	$103.65	12.588%	$116.6975	$116.70	$116.70	$116.70
Purchase #4	$85.47	7.638%	$91.9982	$92.00	$92.00	$92.00
Purchase #5	$111.29	8.267%	$120.4903	$120.49	$120.50	$120.50
Purchase #6	$64.87	11.240%	$72.1614	$72.16	$72.15	$72.20
Purchase #7	$47.34	6.760%	$50.5402	$50.54	$50.55	$50.50
7 purchase totals =	$679.33		$737.9802	$737.98	$738.00	$738.00