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	$206.73	5.213%	$217.5068	$217.51	$217.50	$217.50
Purchase #2	$145.52	11.204%	$161.8241	$161.82	$161.80	$161.80
Purchase #3	$78.52	4.459%	$82.0212	$82.02	$82.00	$82.00
Purchase #4	$76.89	7.219%	$82.4407	$82.44	$82.45	$82.40
Purchase #5	$184.50	13.548%	$209.4961	$209.50	$209.50	$209.50
Purchase #6	$84.32	8.648%	$91.612	$91.61	$91.60	$91.60
Purchase #7	$202.34	11.433%	$225.4735	$225.47	$225.45	$225.50
7 purchase totals =	$978.82		$1,070.3744	$1,070.37	$1,070.30	$1,070.30