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	$9.25	12.311%	$10.3888	$10.39	$10.40	$10.40
Purchase #2	$165.37	7.308%	$177.4552	$177.46	$177.45	$177.50
Purchase #3	$111.73	9.412%	$122.246	$122.25	$122.25	$122.20
Purchase #4	$92.34	7.737%	$99.4843	$99.48	$99.50	$99.50
Purchase #5	$68.40	13.248%	$77.4616	$77.46	$77.45	$77.50
Purchase #6	$30.59	7.470%	$32.8751	$32.88	$32.90	$32.90
Purchase #7	$9.30	13.781%	$10.5816	$10.58	$10.60	$10.60
7 purchase totals =	$486.98		$530.4926	$530.50	$530.55	$530.60