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	$135.43	12.500%	$152.3588	$152.36	$152.35	$152.40
Purchase #2	$212.41	8.301%	$230.0422	$230.04	$230.05	$230.00
Purchase #3	$227.85	7.392%	$244.6927	$244.69	$244.70	$244.70
Purchase #4	$40.59	3.776%	$42.1227	$42.12	$42.10	$42.10
Purchase #5	$54.66	12.754%	$61.6313	$61.63	$61.65	$61.60
Purchase #6	$13.96	9.805%	$15.3288	$15.33	$15.35	$15.30
Purchase #7	$249.90	13.814%	$284.4212	$284.42	$284.40	$284.40
7 purchase totals =	$934.80		$1,030.5977	$1,030.59	$1,030.60	$1,030.50