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	$103.52	12.766%	$116.7354	$116.74	$116.75	$116.70
Purchase #2	$159.52	8.275%	$172.7203	$172.72	$172.70	$172.70
Purchase #3	$200.54	13.306%	$227.2239	$227.22	$227.20	$227.20
Purchase #4	$154.58	9.208%	$168.8137	$168.81	$168.80	$168.80
Purchase #5	$15.42	9.590%	$16.8988	$16.90	$16.90	$16.90
Purchase #6	$191.71	8.508%	$208.0207	$208.02	$208.00	$208.00
Purchase #7	$138.96	4.298%	$144.9325	$144.93	$144.95	$144.90
7 purchase totals =	$964.25		$1,055.3453	$1,055.34	$1,055.30	$1,055.20