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	$89.30	11.596%	$99.6552	$99.66	$99.65	$99.70
Purchase #2	$69.86	12.381%	$78.5094	$78.51	$78.50	$78.50
Purchase #3	$48.31	11.864%	$54.0415	$54.04	$54.05	$54.00
Purchase #4	$138.33	4.195%	$144.1329	$144.13	$144.15	$144.10
Purchase #5	$88.48	5.362%	$93.2243	$93.22	$93.20	$93.20
Purchase #6	$39.39	6.307%	$41.8743	$41.87	$41.85	$41.90
Purchase #7	$152.60	5.475%	$160.9549	$160.95	$160.95	$161.00
7 purchase totals =	$626.27		$672.3925	$672.38	$672.35	$672.40