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	$33.57	12.591%	$37.7968	$37.80	$37.80	$37.80
Purchase #2	$140.72	13.150%	$159.2247	$159.22	$159.20	$159.20
Purchase #3	$93.82	10.784%	$103.9375	$103.94	$103.95	$103.90
Purchase #4	$217.69	10.846%	$241.3007	$241.30	$241.30	$241.30
Purchase #5	$224.56	3.836%	$233.1741	$233.17	$233.15	$233.20
Purchase #6	$10.67	12.275%	$11.9797	$11.98	$12.00	$12.00
Purchase #7	$243.35	13.503%	$276.2096	$276.21	$276.20	$276.20
7 purchase totals =	$964.38		$1,063.6231	$1,063.62	$1,063.60	$1,063.60