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	$122.75	6.322%	$130.5103	$130.51	$130.50	$130.50
Purchase #2	$143.45	13.215%	$162.4069	$162.41	$162.40	$162.40
Purchase #3	$143.47	5.268%	$151.028	$151.03	$151.05	$151.00
Purchase #4	$17.63	4.667%	$18.4528	$18.45	$18.45	$18.50
Purchase #5	$73.77	13.607%	$83.8079	$83.81	$83.80	$83.80
Purchase #6	$132.98	8.644%	$144.4748	$144.47	$144.45	$144.50
Purchase #7	$105.65	6.697%	$112.7254	$112.73	$112.75	$112.70
7 purchase totals =	$739.70		$803.4061	$803.41	$803.40	$803.40