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	$170.27	11.750%	$190.2767	$190.28	$190.30	$190.30
Purchase #2	$81.39	11.700%	$90.9126	$90.91	$90.90	$90.90
Purchase #3	$116.33	13.724%	$132.2951	$132.30	$132.30	$132.30
Purchase #4	$123.30	10.381%	$136.0998	$136.10	$136.10	$136.10
Purchase #5	$131.65	11.410%	$146.6713	$146.67	$146.65	$146.70
Purchase #6	$36.28	8.440%	$39.342	$39.34	$39.35	$39.30
Purchase #7	$231.95	7.607%	$249.5944	$249.59	$249.60	$249.60
7 purchase totals =	$891.17		$985.1919	$985.19	$985.20	$985.20