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	$37.77	5.133%	$39.7087	$39.71	$39.70	$39.70
Purchase #2	$52.36	10.503%	$57.8594	$57.86	$57.85	$57.90
Purchase #3	$231.28	9.664%	$253.6309	$253.63	$253.65	$253.60
Purchase #4	$35.55	5.133%	$37.3748	$37.37	$37.35	$37.40
Purchase #5	$104.95	6.863%	$112.1527	$112.15	$112.15	$112.20
Purchase #6	$29.45	12.795%	$33.2181	$33.22	$33.20	$33.20
Purchase #7	$36.91	13.453%	$41.8755	$41.88	$41.90	$41.90
7 purchase totals =	$528.27		$575.8201	$575.82	$575.80	$575.90