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	$37.64	13.501%	$42.7218	$42.72	$42.70	$42.70
Purchase #2	$29.55	12.492%	$33.2414	$33.24	$33.25	$33.20
Purchase #3	$38.39	4.627%	$40.1663	$40.17	$40.15	$40.20
Purchase #4	$157.92	4.812%	$165.5191	$165.52	$165.50	$165.50
Purchase #5	$127.70	11.158%	$141.9488	$141.95	$141.95	$141.90
Purchase #6	$32.44	4.588%	$33.9283	$33.93	$33.95	$33.90
Purchase #7	$169.41	13.119%	$191.6349	$191.63	$191.65	$191.60
7 purchase totals =	$593.05		$649.1606	$649.16	$649.15	$649.00