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	$18.98	13.397%	$21.5228	$21.52	$21.50	$21.50
Purchase #2	$234.61	13.281%	$265.7686	$265.77	$265.75	$265.80
Purchase #3	$208.37	4.738%	$218.2426	$218.24	$218.25	$218.20
Purchase #4	$143.60	8.598%	$155.9467	$155.95	$155.95	$155.90
Purchase #5	$23.72	3.747%	$24.6088	$24.61	$24.60	$24.60
Purchase #6	$248.48	6.371%	$264.3107	$264.31	$264.30	$264.30
Purchase #7	$139.63	3.606%	$144.6651	$144.67	$144.65	$144.70
7 purchase totals =	$1,017.39		$1,095.0653	$1,095.07	$1,095.00	$1,095.00