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	$66.43	6.460%	$70.7214	$70.72	$70.70	$70.70
Purchase #2	$39.81	5.683%	$42.0724	$42.07	$42.05	$42.10
Purchase #3	$88.86	13.140%	$100.5362	$100.54	$100.55	$100.50
Purchase #4	$148.62	11.668%	$165.961	$165.96	$165.95	$166.00
Purchase #5	$45.27	9.389%	$49.5204	$49.52	$49.50	$49.50
Purchase #6	$206.28	6.297%	$219.2695	$219.27	$219.25	$219.30
Purchase #7	$22.93	7.805%	$24.7197	$24.72	$24.70	$24.70
7 purchase totals =	$618.20		$672.8006	$672.80	$672.70	$672.80