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	$33.52	8.841%	$36.4835	$36.48	$36.50	$36.50
Purchase #2	$204.85	11.581%	$228.5737	$228.57	$228.55	$228.60
Purchase #3	$111.80	10.148%	$123.1455	$123.15	$123.15	$123.10
Purchase #4	$141.61	11.672%	$158.1387	$158.14	$158.15	$158.10
Purchase #5	$208.43	4.802%	$218.4388	$218.44	$218.45	$218.40
Purchase #6	$200.66	10.680%	$222.0905	$222.09	$222.10	$222.10
Purchase #7	$40.41	13.204%	$45.7457	$45.75	$45.75	$45.70
7 purchase totals =	$941.28		$1,032.6164	$1,032.62	$1,032.65	$1,032.50