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	$11.87	10.827%	$13.1552	$13.16	$13.15	$13.20
Purchase #2	$71.28	10.718%	$78.9198	$78.92	$78.90	$78.90
Purchase #3	$54.42	4.603%	$56.925	$56.93	$56.95	$56.90
Purchase #4	$114.59	13.542%	$130.1078	$130.11	$130.10	$130.10
Purchase #5	$154.57	7.697%	$166.4673	$166.47	$166.45	$166.50
Purchase #6	$223.37	12.641%	$251.6062	$251.61	$251.60	$251.60
Purchase #7	$138.71	12.294%	$155.763	$155.76	$155.75	$155.80
7 purchase totals =	$768.81		$852.9443	$852.96	$852.90	$853.00