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	$235.56	6.630%	$251.1776	$251.18	$251.20	$251.20
Purchase #2	$100.55	11.347%	$111.9594	$111.96	$111.95	$112.00
Purchase #3	$155.30	6.840%	$165.9225	$165.92	$165.90	$165.90
Purchase #4	$144.61	5.251%	$152.2035	$152.20	$152.20	$152.20
Purchase #5	$10.37	6.429%	$11.0367	$11.04	$11.05	$11.00
Purchase #6	$25.84	10.717%	$28.6093	$28.61	$28.60	$28.60
Purchase #7	$152.74	13.172%	$172.8589	$172.86	$172.85	$172.90
7 purchase totals =	$824.97		$893.7679	$893.77	$893.75	$893.80