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	$14.43	7.864%	$15.5648	$15.56	$15.55	$15.60
Purchase #2	$118.54	8.305%	$128.3847	$128.38	$128.40	$128.40
Purchase #3	$110.72	11.482%	$123.4329	$123.43	$123.45	$123.40
Purchase #4	$146.36	10.580%	$161.8449	$161.84	$161.85	$161.80
Purchase #5	$165.49	4.678%	$173.2316	$173.23	$173.25	$173.20
Purchase #6	$42.29	6.679%	$45.1145	$45.11	$45.10	$45.10
Purchase #7	$37.68	5.320%	$39.6846	$39.68	$39.70	$39.70
7 purchase totals =	$635.51		$687.2580	$687.23	$687.30	$687.20