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	$218.37	7.297%	$234.3045	$234.30	$234.30	$234.30
Purchase #2	$200.49	11.466%	$223.4782	$223.48	$223.50	$223.50
Purchase #3	$43.46	9.324%	$47.5122	$47.51	$47.50	$47.50
Purchase #4	$33.68	12.353%	$37.8405	$37.84	$37.85	$37.80
Purchase #5	$32.39	4.167%	$33.7397	$33.74	$33.75	$33.70
Purchase #6	$55.32	10.175%	$60.9488	$60.95	$60.95	$60.90
Purchase #7	$154.72	7.353%	$166.0966	$166.10	$166.10	$166.10
7 purchase totals =	$738.43		$803.9205	$803.92	$803.95	$803.80