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	$99.68	4.232%	$103.8985	$103.90	$103.90	$103.90
Purchase #2	$59.74	12.497%	$67.2057	$67.21	$67.20	$67.20
Purchase #3	$40.89	11.326%	$45.5212	$45.52	$45.50	$45.50
Purchase #4	$22.59	9.414%	$24.7166	$24.72	$24.70	$24.70
Purchase #5	$65.53	13.578%	$74.4277	$74.43	$74.45	$74.40
Purchase #6	$182.30	8.795%	$198.3333	$198.33	$198.35	$198.30
Purchase #7	$153.81	7.626%	$165.5396	$165.54	$165.55	$165.50
7 purchase totals =	$624.54		$679.6426	$679.65	$679.65	$679.50