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	$54.54	8.573%	$59.2157	$59.22	$59.20	$59.20
Purchase #2	$126.78	7.733%	$136.5839	$136.58	$136.60	$136.60
Purchase #3	$197.77	5.856%	$209.3514	$209.35	$209.35	$209.40
Purchase #4	$78.96	4.736%	$82.6995	$82.70	$82.70	$82.70
Purchase #5	$41.80	11.287%	$46.518	$46.52	$46.50	$46.50
Purchase #6	$108.27	8.293%	$117.2488	$117.25	$117.25	$117.20
Purchase #7	$158.37	7.628%	$170.4505	$170.45	$170.45	$170.50
7 purchase totals =	$766.49		$822.0678	$822.07	$822.05	$822.10