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	$159.86	3.396%	$165.2888	$165.29	$165.30	$165.30
Purchase #2	$103.46	6.549%	$110.2356	$110.24	$110.25	$110.20
Purchase #3	$154.38	11.436%	$172.0349	$172.03	$172.05	$172.00
Purchase #4	$111.40	12.134%	$124.9173	$124.92	$124.90	$124.90
Purchase #5	$243.82	6.781%	$260.3534	$260.35	$260.35	$260.40
Purchase #6	$50.59	10.111%	$55.7052	$55.71	$55.70	$55.70
Purchase #7	$18.78	12.500%	$21.1275	$21.13	$21.15	$21.10
7 purchase totals =	$842.29		$909.6627	$909.67	$909.70	$909.60