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	$93.39	13.274%	$105.7866	$105.79	$105.80	$105.80
Purchase #2	$172.83	4.394%	$180.4242	$180.42	$180.40	$180.40
Purchase #3	$84.38	8.473%	$91.5295	$91.53	$91.55	$91.50
Purchase #4	$50.70	8.569%	$55.0445	$55.04	$55.05	$55.00
Purchase #5	$149.71	3.139%	$154.4094	$154.41	$154.40	$154.40
Purchase #6	$178.83	11.570%	$199.5206	$199.52	$199.50	$199.50
Purchase #7	$148.61	7.262%	$159.4021	$159.40	$159.40	$159.40
7 purchase totals =	$878.45		$946.1169	$946.11	$946.10	$946.00