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	$104.43	12.626%	$117.6153	$117.62	$117.60	$117.60
Purchase #2	$88.47	13.717%	$100.6054	$100.61	$100.60	$100.60
Purchase #3	$137.62	4.560%	$143.8955	$143.90	$143.90	$143.90
Purchase #4	$92.85	10.344%	$102.4544	$102.45	$102.45	$102.50
Purchase #5	$11.79	5.849%	$12.4796	$12.48	$12.50	$12.50
Purchase #6	$166.75	7.674%	$179.5464	$179.55	$179.55	$179.50
Purchase #7	$197.42	8.547%	$214.2935	$214.29	$214.30	$214.30
7 purchase totals =	$799.33		$870.8901	$870.90	$870.90	$870.90