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	$17.72	3.509%	$18.3418	$18.34	$18.35	$18.30
Purchase #2	$222.57	12.121%	$249.5477	$249.55	$249.55	$249.50
Purchase #3	$25.59	7.371%	$27.4762	$27.48	$27.50	$27.50
Purchase #4	$132.88	11.476%	$148.1293	$148.13	$148.15	$148.10
Purchase #5	$180.40	10.664%	$199.6379	$199.64	$199.65	$199.60
Purchase #6	$40.91	5.291%	$43.0745	$43.07	$43.05	$43.10
Purchase #7	$97.26	11.872%	$108.8067	$108.81	$108.80	$108.80
7 purchase totals =	$717.33		$795.0141	$795.02	$795.05	$794.90