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	$28.74	12.707%	$32.392	$32.39	$32.40	$32.40
Purchase #2	$122.29	6.513%	$130.2547	$130.25	$130.25	$130.30
Purchase #3	$121.36	8.362%	$131.5081	$131.51	$131.50	$131.50
Purchase #4	$149.84	8.672%	$162.8341	$162.83	$162.85	$162.80
Purchase #5	$40.85	4.181%	$42.5579	$42.56	$42.55	$42.60
Purchase #6	$67.72	3.720%	$70.2392	$70.24	$70.25	$70.20
Purchase #7	$97.72	13.305%	$110.7216	$110.72	$110.70	$110.70
7 purchase totals =	$628.52		$680.5076	$680.50	$680.50	$680.50