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	$36.72	7.394%	$39.4351	$39.44	$39.45	$39.40
Purchase #2	$233.79	11.594%	$260.8956	$260.90	$260.90	$260.90
Purchase #3	$202.76	10.334%	$223.7132	$223.71	$223.70	$223.70
Purchase #4	$150.25	11.778%	$167.9464	$167.95	$167.95	$167.90
Purchase #5	$46.60	8.716%	$50.6617	$50.66	$50.65	$50.70
Purchase #6	$160.83	7.457%	$172.8231	$172.82	$172.80	$172.80
Purchase #7	$48.65	11.137%	$54.0682	$54.07	$54.05	$54.10
7 purchase totals =	$879.60		$969.5433	$969.55	$969.50	$969.50