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	$122.47	4.647%	$128.1612	$128.16	$128.15	$128.20
Purchase #2	$85.85	10.113%	$94.532	$94.53	$94.55	$94.50
Purchase #3	$150.37	13.342%	$170.4324	$170.43	$170.45	$170.40
Purchase #4	$183.35	7.417%	$196.9491	$196.95	$196.95	$196.90
Purchase #5	$138.26	5.520%	$145.892	$145.89	$145.90	$145.90
Purchase #6	$85.70	7.316%	$91.9698	$91.97	$91.95	$92.00
Purchase #7	$9.50	9.443%	$10.3971	$10.40	$10.40	$10.40
7 purchase totals =	$775.50		$838.3336	$838.33	$838.35	$838.30