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	$8.34	10.387%	$9.2063	$9.21	$9.20	$9.20
Purchase #2	$42.38	7.563%	$45.5852	$45.59	$45.60	$45.60
Purchase #3	$194.67	9.426%	$213.0196	$213.02	$213.00	$213.00
Purchase #4	$35.55	5.393%	$37.4672	$37.47	$37.45	$37.50
Purchase #5	$9.40	13.590%	$10.6775	$10.68	$10.70	$10.70
Purchase #6	$196.50	13.765%	$223.5482	$223.55	$223.55	$223.50
Purchase #7	$59.66	12.785%	$67.2875	$67.29	$67.30	$67.30
7 purchase totals =	$546.50		$606.7915	$606.81	$606.80	$606.80