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	$112.96	13.569%	$128.2875	$128.29	$128.30	$128.30
Purchase #2	$243.42	7.244%	$261.0533	$261.05	$261.05	$261.10
Purchase #3	$227.96	10.335%	$251.5197	$251.52	$251.50	$251.50
Purchase #4	$44.28	13.610%	$50.3065	$50.31	$50.30	$50.30
Purchase #5	$80.30	3.569%	$83.1659	$83.17	$83.15	$83.20
Purchase #6	$37.84	6.874%	$40.4411	$40.44	$40.45	$40.40
Purchase #7	$144.57	4.287%	$150.7677	$150.77	$150.75	$150.80
7 purchase totals =	$891.33		$965.5417	$965.55	$965.50	$965.60