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	$244.80	12.862%	$276.2862	$276.29	$276.30	$276.30
Purchase #2	$34.90	4.208%	$36.3686	$36.37	$36.35	$36.40
Purchase #3	$129.83	12.287%	$145.7822	$145.78	$145.80	$145.80
Purchase #4	$135.43	8.411%	$146.821	$146.82	$146.80	$146.80
Purchase #5	$194.65	7.318%	$208.8945	$208.89	$208.90	$208.90
Purchase #6	$250.47	13.735%	$284.8721	$284.87	$284.85	$284.90
Purchase #7	$9.86	5.487%	$10.401	$10.40	$10.40	$10.40
7 purchase totals =	$999.94		$1,109.4256	$1,109.42	$1,109.40	$1,109.50