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	$133.87	3.521%	$138.5836	$138.58	$138.60	$138.60
Purchase #2	$33.65	8.585%	$36.5389	$36.54	$36.55	$36.50
Purchase #3	$164.77	12.766%	$185.8045	$185.80	$185.80	$185.80
Purchase #4	$63.84	12.634%	$71.9055	$71.91	$71.90	$71.90
Purchase #5	$38.31	9.733%	$42.0387	$42.04	$42.05	$42.00
Purchase #6	$104.90	8.500%	$113.8165	$113.82	$113.80	$113.80
Purchase #7	$91.39	4.814%	$95.7895	$95.79	$95.80	$95.80
7 purchase totals =	$630.73		$684.4772	$684.48	$684.50	$684.40