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	$32.61	3.395%	$33.7171	$33.72	$33.70	$33.70
Purchase #2	$47.42	11.568%	$52.9055	$52.91	$52.90	$52.90
Purchase #3	$197.31	13.828%	$224.594	$224.59	$224.60	$224.60
Purchase #4	$85.25	11.209%	$94.8057	$94.81	$94.80	$94.80
Purchase #5	$133.71	6.592%	$142.5242	$142.52	$142.50	$142.50
Purchase #6	$184.39	8.849%	$200.7067	$200.71	$200.70	$200.70
Purchase #7	$123.94	3.624%	$128.4316	$128.43	$128.45	$128.40
7 purchase totals =	$804.63		$877.6848	$877.69	$877.65	$877.60