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	$9.28	10.265%	$10.2326	$10.23	$10.25	$10.20
Purchase #2	$40.33	6.278%	$42.8619	$42.86	$42.85	$42.90
Purchase #3	$65.52	13.282%	$74.2224	$74.22	$74.20	$74.20
Purchase #4	$161.50	6.788%	$172.4626	$172.46	$172.45	$172.50
Purchase #5	$80.69	13.555%	$91.6275	$91.63	$91.65	$91.60
Purchase #6	$234.82	13.460%	$266.4268	$266.43	$266.45	$266.40
Purchase #7	$18.77	11.680%	$20.9623	$20.96	$20.95	$21.00
7 purchase totals =	$610.91		$678.7961	$678.79	$678.80	$678.80