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	$36.40	3.188%	$37.5604	$37.56	$37.55	$37.60
Purchase #2	$232.50	10.169%	$256.1429	$256.14	$256.15	$256.10
Purchase #3	$91.40	9.181%	$99.7914	$99.79	$99.80	$99.80
Purchase #4	$95.29	8.189%	$103.0933	$103.09	$103.10	$103.10
Purchase #5	$192.70	9.790%	$211.5653	$211.57	$211.55	$211.60
Purchase #6	$23.91	6.698%	$25.5115	$25.51	$25.50	$25.50
Purchase #7	$35.48	10.821%	$39.3193	$39.32	$39.30	$39.30
7 purchase totals =	$707.68		$772.9841	$772.98	$772.95	$773.00