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	$250.31	13.313%	$283.6338	$283.63	$283.65	$283.60
Purchase #2	$154.50	9.523%	$169.213	$169.21	$169.20	$169.20
Purchase #3	$160.99	6.485%	$171.4302	$171.43	$171.45	$171.40
Purchase #4	$55.31	11.700%	$61.7813	$61.78	$61.80	$61.80
Purchase #5	$213.66	13.282%	$242.0383	$242.04	$242.05	$242.00
Purchase #6	$55.35	4.197%	$57.673	$57.67	$57.65	$57.70
Purchase #7	$78.88	8.808%	$85.8278	$85.83	$85.85	$85.80
7 purchase totals =	$969.00		$1,071.5974	$1,071.59	$1,071.65	$1,071.50