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	$57.32	3.131%	$59.1147	$59.11	$59.10	$59.10
Purchase #2	$166.80	11.104%	$185.3215	$185.32	$185.30	$185.30
Purchase #3	$140.70	9.204%	$153.65	$153.65	$153.65	$153.70
Purchase #4	$138.37	9.698%	$151.7891	$151.79	$151.80	$151.80
Purchase #5	$217.88	7.605%	$234.4498	$234.45	$234.45	$234.40
Purchase #6	$58.60	5.540%	$61.8464	$61.85	$61.85	$61.80
Purchase #7	$67.72	11.214%	$75.3141	$75.31	$75.30	$75.30
7 purchase totals =	$847.39		$921.4856	$921.48	$921.45	$921.40