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	$40.50	12.122%	$45.4094	$45.41	$45.40	$45.40
Purchase #2	$48.79	7.172%	$52.2892	$52.29	$52.30	$52.30
Purchase #3	$11.25	4.248%	$11.7279	$11.73	$11.75	$11.70
Purchase #4	$44.40	12.312%	$49.8665	$49.87	$49.85	$49.90
Purchase #5	$9.31	10.586%	$10.2956	$10.30	$10.30	$10.30
Purchase #6	$158.69	7.707%	$170.9202	$170.92	$170.90	$170.90
Purchase #7	$36.56	10.187%	$40.2844	$40.28	$40.30	$40.30
7 purchase totals =	$349.50		$380.7932	$380.80	$380.80	$380.80