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	$87.70	13.410%	$99.4606	$99.46	$99.45	$99.50
Purchase #2	$115.78	4.500%	$120.9901	$120.99	$121.00	$121.00
Purchase #3	$16.94	6.512%	$18.0431	$18.04	$18.05	$18.00
Purchase #4	$42.25	8.533%	$45.8552	$45.86	$45.85	$45.90
Purchase #5	$13.97	10.707%	$15.4658	$15.47	$15.45	$15.50
Purchase #6	$16.86	13.704%	$19.1705	$19.17	$19.15	$19.20
Purchase #7	$56.52	10.610%	$62.5168	$62.52	$62.50	$62.50
7 purchase totals =	$350.02		$381.5021	$381.51	$381.45	$381.60