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	$40.38	13.504%	$45.8329	$45.83	$45.85	$45.80
Purchase #2	$234.79	8.452%	$254.6345	$254.63	$254.65	$254.60
Purchase #3	$221.80	12.334%	$249.1568	$249.16	$249.15	$249.20
Purchase #4	$125.92	10.508%	$139.1517	$139.15	$139.15	$139.20
Purchase #5	$121.40	8.621%	$131.8659	$131.87	$131.85	$131.90
Purchase #6	$13.70	11.586%	$15.2873	$15.29	$15.30	$15.30
Purchase #7	$71.25	13.567%	$80.9165	$80.92	$80.90	$80.90
7 purchase totals =	$829.24		$916.8456	$916.85	$916.85	$916.90