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	$90.30	10.627%	$99.8962	$99.90	$99.90	$99.90
Purchase #2	$60.35	9.414%	$66.0313	$66.03	$66.05	$66.00
Purchase #3	$188.25	11.450%	$209.8046	$209.80	$209.80	$209.80
Purchase #4	$25.95	7.469%	$27.8882	$27.89	$27.90	$27.90
Purchase #5	$153.37	9.394%	$167.7776	$167.78	$167.80	$167.80
Purchase #6	$208.81	8.253%	$226.0431	$226.04	$226.05	$226.00
Purchase #7	$11.87	5.374%	$12.5079	$12.51	$12.50	$12.50
7 purchase totals =	$738.90		$809.9489	$809.95	$810.00	$809.90