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	$135.78	9.862%	$149.1706	$149.17	$149.15	$149.20
Purchase #2	$50.93	8.466%	$55.2417	$55.24	$55.25	$55.20
Purchase #3	$9.41	7.629%	$10.1279	$10.13	$10.15	$10.10
Purchase #4	$227.69	12.610%	$256.4017	$256.40	$256.40	$256.40
Purchase #5	$51.55	11.404%	$57.4288	$57.43	$57.45	$57.40
Purchase #6	$57.50	3.260%	$59.3745	$59.37	$59.35	$59.40
Purchase #7	$121.72	3.162%	$125.5688	$125.57	$125.55	$125.60
7 purchase totals =	$654.58		$713.3140	$713.31	$713.30	$713.30