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	$81.33	11.203%	$90.4414	$90.44	$90.45	$90.40
Purchase #2	$20.38	8.165%	$22.044	$22.04	$22.05	$22.00
Purchase #3	$34.85	10.449%	$38.4915	$38.49	$38.50	$38.50
Purchase #4	$43.55	11.743%	$48.6641	$48.66	$48.65	$48.70
Purchase #5	$43.96	10.676%	$48.6532	$48.65	$48.65	$48.70
Purchase #6	$176.43	12.164%	$197.8909	$197.89	$197.90	$197.90
Purchase #7	$44.25	13.726%	$50.3238	$50.32	$50.30	$50.30
7 purchase totals =	$444.75		$496.5089	$496.49	$496.50	$496.50