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	$41.90	6.727%	$44.7186	$44.72	$44.70	$44.70
Purchase #2	$155.77	6.319%	$165.6131	$165.61	$165.60	$165.60
Purchase #3	$18.45	11.294%	$20.5337	$20.53	$20.55	$20.50
Purchase #4	$66.86	7.513%	$71.8832	$71.88	$71.90	$71.90
Purchase #5	$235.92	12.300%	$264.9382	$264.94	$264.95	$264.90
Purchase #6	$228.57	12.770%	$257.7584	$257.76	$257.75	$257.80
Purchase #7	$122.31	7.205%	$131.1224	$131.12	$131.10	$131.10
7 purchase totals =	$869.78		$956.5676	$956.56	$956.55	$956.50