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	$198.98	12.342%	$223.5381	$223.54	$223.55	$223.50
Purchase #2	$67.35	5.199%	$70.8515	$70.85	$70.85	$70.90
Purchase #3	$244.30	13.681%	$277.7227	$277.72	$277.70	$277.70
Purchase #4	$75.84	10.667%	$83.9299	$83.93	$83.95	$83.90
Purchase #5	$119.42	4.251%	$124.4965	$124.50	$124.50	$124.50
Purchase #6	$112.30	13.483%	$127.4414	$127.44	$127.45	$127.40
Purchase #7	$32.70	6.634%	$34.8693	$34.87	$34.85	$34.90
7 purchase totals =	$850.89		$942.8494	$942.85	$942.85	$942.80