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	$34.35	12.475%	$38.6352	$38.64	$38.65	$38.60
Purchase #2	$204.60	4.140%	$213.0704	$213.07	$213.05	$213.10
Purchase #3	$39.34	9.386%	$43.0325	$43.03	$43.05	$43.00
Purchase #4	$141.63	9.686%	$155.3483	$155.35	$155.35	$155.30
Purchase #5	$94.39	10.352%	$104.1613	$104.16	$104.15	$104.20
Purchase #6	$52.96	10.848%	$58.7051	$58.71	$58.70	$58.70
Purchase #7	$55.77	6.680%	$59.4954	$59.50	$59.50	$59.50
7 purchase totals =	$623.04		$672.4482	$672.46	$672.45	$672.40