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	$39.93	6.103%	$42.3669	$42.37	$42.35	$42.40
Purchase #2	$126.57	11.217%	$140.7674	$140.77	$140.75	$140.80
Purchase #3	$19.31	6.512%	$20.5675	$20.57	$20.55	$20.60
Purchase #4	$46.73	8.660%	$50.7768	$50.78	$50.80	$50.80
Purchase #5	$204.93	10.137%	$225.7038	$225.70	$225.70	$225.70
Purchase #6	$62.38	3.634%	$64.6469	$64.65	$64.65	$64.60
Purchase #7	$59.94	4.226%	$62.4731	$62.47	$62.45	$62.50
7 purchase totals =	$559.79		$607.3024	$607.31	$607.25	$607.40