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	$65.54	7.156%	$70.23	$70.23	$70.25	$70.20
Purchase #2	$222.29	13.651%	$252.6348	$252.63	$252.65	$252.60
Purchase #3	$9.89	10.449%	$10.9234	$10.92	$10.90	$10.90
Purchase #4	$166.85	10.418%	$184.2324	$184.23	$184.25	$184.20
Purchase #5	$59.89	11.193%	$66.5935	$66.59	$66.60	$66.60
Purchase #6	$216.54	5.490%	$228.428	$228.43	$228.45	$228.40
Purchase #7	$37.90	12.641%	$42.6909	$42.69	$42.70	$42.70
7 purchase totals =	$778.90		$855.7330	$855.72	$855.80	$855.60