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	$45.78	8.472%	$49.6585	$49.66	$49.65	$49.70
Purchase #2	$50.31	3.764%	$52.2037	$52.20	$52.20	$52.20
Purchase #3	$37.81	13.186%	$42.7956	$42.80	$42.80	$42.80
Purchase #4	$151.74	11.522%	$169.2235	$169.22	$169.20	$169.20
Purchase #5	$82.87	9.708%	$90.915	$90.92	$90.90	$90.90
Purchase #6	$92.75	9.381%	$101.4509	$101.45	$101.45	$101.50
Purchase #7	$146.51	13.514%	$166.3094	$166.31	$166.30	$166.30
7 purchase totals =	$607.77		$672.5566	$672.56	$672.50	$672.60