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	$218.55	13.337%	$247.698	$247.70	$247.70	$247.70
Purchase #2	$132.29	6.699%	$141.1521	$141.15	$141.15	$141.20
Purchase #3	$77.77	10.385%	$85.8464	$85.85	$85.85	$85.80
Purchase #4	$59.99	3.430%	$62.0477	$62.05	$62.05	$62.00
Purchase #5	$91.31	10.111%	$100.5424	$100.54	$100.55	$100.50
Purchase #6	$39.82	11.149%	$44.2595	$44.26	$44.25	$44.30
Purchase #7	$130.50	11.244%	$145.1734	$145.17	$145.15	$145.20
7 purchase totals =	$750.23		$826.7195	$826.72	$826.70	$826.70