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	$131.41	11.228%	$146.1647	$146.16	$146.15	$146.20
Purchase #2	$200.85	9.406%	$219.742	$219.74	$219.75	$219.70
Purchase #3	$41.72	9.386%	$45.6358	$45.64	$45.65	$45.60
Purchase #4	$12.73	11.660%	$14.2143	$14.21	$14.20	$14.20
Purchase #5	$19.29	11.274%	$21.4648	$21.46	$21.45	$21.50
Purchase #6	$72.61	8.433%	$78.7332	$78.73	$78.75	$78.70
Purchase #7	$195.81	10.806%	$216.9692	$216.97	$216.95	$217.00
7 purchase totals =	$674.42		$742.9240	$742.91	$742.90	$742.90