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	$149.57	4.178%	$155.819	$155.82	$155.80	$155.80
Purchase #2	$166.50	13.119%	$188.3431	$188.34	$188.35	$188.30
Purchase #3	$172.89	4.526%	$180.715	$180.72	$180.70	$180.70
Purchase #4	$52.51	9.317%	$57.4024	$57.40	$57.40	$57.40
Purchase #5	$83.92	7.356%	$90.0932	$90.09	$90.10	$90.10
Purchase #6	$9.72	7.374%	$10.4368	$10.44	$10.45	$10.40
Purchase #7	$235.85	7.460%	$253.4444	$253.44	$253.45	$253.40
7 purchase totals =	$870.96		$936.2539	$936.25	$936.25	$936.10