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	$60.65	9.164%	$66.208	$66.21	$66.20	$66.20
Purchase #2	$182.35	5.208%	$191.8468	$191.85	$191.85	$191.80
Purchase #3	$34.90	6.847%	$37.2896	$37.29	$37.30	$37.30
Purchase #4	$193.63	11.301%	$215.5121	$215.51	$215.50	$215.50
Purchase #5	$53.53	3.133%	$55.2071	$55.21	$55.20	$55.20
Purchase #6	$171.80	3.790%	$178.3112	$178.31	$178.30	$178.30
Purchase #7	$141.34	7.141%	$151.4331	$151.43	$151.45	$151.40
7 purchase totals =	$838.20		$895.8079	$895.81	$895.80	$895.70