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	$18.44	12.828%	$20.8055	$20.81	$20.80	$20.80
Purchase #2	$19.37	10.742%	$21.4507	$21.45	$21.45	$21.50
Purchase #3	$231.50	10.634%	$256.1177	$256.12	$256.10	$256.10
Purchase #4	$47.25	8.726%	$51.373	$51.37	$51.35	$51.40
Purchase #5	$57.37	13.503%	$65.1167	$65.12	$65.10	$65.10
Purchase #6	$13.89	8.467%	$15.0661	$15.07	$15.05	$15.10
Purchase #7	$45.91	13.844%	$52.2658	$52.27	$52.25	$52.30
7 purchase totals =	$433.73		$482.1955	$482.21	$482.10	$482.30