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	$35.55	12.259%	$39.9081	$39.91	$39.90	$39.90
Purchase #2	$231.82	6.504%	$246.8976	$246.90	$246.90	$246.90
Purchase #3	$137.28	13.111%	$155.2788	$155.28	$155.30	$155.30
Purchase #4	$119.64	5.214%	$125.878	$125.88	$125.90	$125.90
Purchase #5	$55.60	9.854%	$61.0788	$61.08	$61.10	$61.10
Purchase #6	$59.35	13.829%	$67.5575	$67.56	$67.55	$67.60
Purchase #7	$237.27	7.697%	$255.5327	$255.53	$255.55	$255.50
7 purchase totals =	$876.51		$952.1315	$952.14	$952.20	$952.20