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	$33.44	13.455%	$37.9394	$37.94	$37.95	$37.90
Purchase #2	$84.48	8.486%	$91.649	$91.65	$91.65	$91.60
Purchase #3	$31.90	4.113%	$33.212	$33.21	$33.20	$33.20
Purchase #4	$38.34	10.778%	$42.4723	$42.47	$42.45	$42.50
Purchase #5	$37.41	8.840%	$40.717	$40.72	$40.70	$40.70
Purchase #6	$87.85	7.691%	$94.6065	$94.61	$94.60	$94.60
Purchase #7	$9.75	7.375%	$10.4691	$10.47	$10.45	$10.50
7 purchase totals =	$323.17		$351.0653	$351.07	$351.00	$351.00