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	$85.77	3.829%	$89.0541	$89.05	$89.05	$89.10
Purchase #2	$27.97	8.306%	$30.2932	$30.29	$30.30	$30.30
Purchase #3	$16.86	12.363%	$18.9444	$18.94	$18.95	$18.90
Purchase #4	$19.39	10.808%	$21.4857	$21.49	$21.50	$21.50
Purchase #5	$123.62	12.507%	$139.0812	$139.08	$139.10	$139.10
Purchase #6	$39.92	13.641%	$45.3655	$45.37	$45.35	$45.40
Purchase #7	$228.39	9.555%	$250.2127	$250.21	$250.20	$250.20
7 purchase totals =	$541.92		$594.4368	$594.43	$594.45	$594.50