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	$47.57	11.690%	$53.1309	$53.13	$53.15	$53.10
Purchase #2	$118.91	9.782%	$130.5418	$130.54	$130.55	$130.50
Purchase #3	$199.27	11.725%	$222.6344	$222.63	$222.65	$222.60
Purchase #4	$11.94	9.761%	$13.1055	$13.11	$13.10	$13.10
Purchase #5	$65.46	8.721%	$71.1688	$71.17	$71.15	$71.20
Purchase #6	$199.71	4.553%	$208.8028	$208.80	$208.80	$208.80
Purchase #7	$170.35	11.811%	$190.47	$190.47	$190.45	$190.50
7 purchase totals =	$813.21		$889.8542	$889.85	$889.85	$889.80