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	$13.93	8.627%	$15.1317	$15.13	$15.15	$15.10
Purchase #2	$114.55	7.817%	$123.5044	$123.50	$123.50	$123.50
Purchase #3	$231.60	11.806%	$258.9427	$258.94	$258.95	$258.90
Purchase #4	$22.32	13.285%	$25.2852	$25.29	$25.30	$25.30
Purchase #5	$83.61	8.294%	$90.5446	$90.54	$90.55	$90.50
Purchase #6	$205.67	7.708%	$221.523	$221.52	$221.50	$221.50
Purchase #7	$40.51	6.621%	$43.1922	$43.19	$43.20	$43.20
7 purchase totals =	$712.19		$778.1238	$778.11	$778.15	$778.00