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	$106.62	13.329%	$120.8314	$120.83	$120.85	$120.80
Purchase #2	$96.72	10.189%	$106.5748	$106.57	$106.55	$106.60
Purchase #3	$217.44	12.692%	$245.0375	$245.04	$245.05	$245.00
Purchase #4	$196.45	4.755%	$205.7912	$205.79	$205.80	$205.80
Purchase #5	$206.83	3.548%	$214.1683	$214.17	$214.15	$214.20
Purchase #6	$86.35	5.487%	$91.088	$91.09	$91.10	$91.10
Purchase #7	$72.35	7.830%	$78.015	$78.02	$78.00	$78.00
7 purchase totals =	$982.76		$1,061.5062	$1,061.51	$1,061.50	$1,061.50