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	$244.67	8.701%	$265.9587	$265.96	$265.95	$266.00
Purchase #2	$89.65	9.554%	$98.2152	$98.22	$98.20	$98.20
Purchase #3	$37.39	13.331%	$42.3745	$42.37	$42.35	$42.40
Purchase #4	$107.34	3.566%	$111.1677	$111.17	$111.15	$111.20
Purchase #5	$14.36	10.172%	$15.8207	$15.82	$15.80	$15.80
Purchase #6	$229.73	7.348%	$246.6106	$246.61	$246.60	$246.60
Purchase #7	$80.71	3.389%	$83.4453	$83.45	$83.45	$83.40
7 purchase totals =	$803.85		$863.5927	$863.60	$863.50	$863.60