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	$11.81	13.680%	$13.4256	$13.43	$13.45	$13.40
Purchase #2	$54.45	5.257%	$57.3124	$57.31	$57.30	$57.30
Purchase #3	$240.32	10.522%	$265.6065	$265.61	$265.60	$265.60
Purchase #4	$132.99	3.570%	$137.7377	$137.74	$137.75	$137.70
Purchase #5	$90.29	9.827%	$99.1628	$99.16	$99.15	$99.20
Purchase #6	$63.73	5.801%	$67.427	$67.43	$67.45	$67.40
Purchase #7	$203.72	9.635%	$223.3484	$223.35	$223.35	$223.30
7 purchase totals =	$797.31		$864.0204	$864.03	$864.05	$863.90