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	$234.47	10.274%	$258.5594	$258.56	$258.55	$258.60
Purchase #2	$39.51	3.388%	$40.8486	$40.85	$40.85	$40.80
Purchase #3	$190.45	4.201%	$198.4508	$198.45	$198.45	$198.50
Purchase #4	$158.79	9.806%	$174.3609	$174.36	$174.35	$174.40
Purchase #5	$141.35	13.355%	$160.2273	$160.23	$160.25	$160.20
Purchase #6	$45.61	13.762%	$51.8868	$51.89	$51.90	$51.90
Purchase #7	$16.30	11.675%	$18.203	$18.20	$18.20	$18.20
7 purchase totals =	$826.48		$902.5368	$902.54	$902.55	$902.60