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	$37.71	13.419%	$42.7703	$42.77	$42.75	$42.80
Purchase #2	$137.55	10.205%	$151.587	$151.59	$151.60	$151.60
Purchase #3	$9.52	7.214%	$10.2068	$10.21	$10.20	$10.20
Purchase #4	$175.81	7.230%	$188.5211	$188.52	$188.50	$188.50
Purchase #5	$146.50	13.841%	$166.7771	$166.78	$166.80	$166.80
Purchase #6	$27.49	6.144%	$29.179	$29.18	$29.20	$29.20
Purchase #7	$77.98	11.855%	$87.2245	$87.22	$87.20	$87.20
7 purchase totals =	$612.56		$676.2658	$676.27	$676.25	$676.30