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	$79.49	12.698%	$89.5836	$89.58	$89.60	$89.60
Purchase #2	$100.78	3.134%	$103.9384	$103.94	$103.95	$103.90
Purchase #3	$14.78	9.308%	$16.1557	$16.16	$16.15	$16.20
Purchase #4	$165.28	6.792%	$176.5058	$176.51	$176.50	$176.50
Purchase #5	$204.67	11.421%	$228.0454	$228.05	$228.05	$228.00
Purchase #6	$42.65	4.590%	$44.6076	$44.61	$44.60	$44.60
Purchase #7	$170.85	11.569%	$190.6156	$190.62	$190.60	$190.60
7 purchase totals =	$778.50		$849.4521	$849.47	$849.45	$849.40