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	$54.57	8.610%	$59.2685	$59.27	$59.25	$59.30
Purchase #2	$233.96	6.597%	$249.3943	$249.39	$249.40	$249.40
Purchase #3	$197.47	11.610%	$220.3963	$220.40	$220.40	$220.40
Purchase #4	$32.75	4.492%	$34.2211	$34.22	$34.20	$34.20
Purchase #5	$118.74	6.815%	$126.8321	$126.83	$126.85	$126.80
Purchase #6	$81.49	10.864%	$90.3431	$90.34	$90.35	$90.30
Purchase #7	$125.85	6.136%	$133.5722	$133.57	$133.55	$133.60
7 purchase totals =	$844.83		$914.0276	$914.02	$914.00	$914.00