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	$111.68	10.518%	$123.4265	$123.43	$123.45	$123.40
Purchase #2	$76.32	5.492%	$80.5115	$80.51	$80.50	$80.50
Purchase #3	$87.88	12.680%	$99.0232	$99.02	$99.00	$99.00
Purchase #4	$223.43	6.733%	$238.4735	$238.47	$238.45	$238.50
Purchase #5	$99.78	11.371%	$111.126	$111.13	$111.15	$111.10
Purchase #6	$218.77	9.751%	$240.1023	$240.10	$240.10	$240.10
Purchase #7	$53.93	13.620%	$61.2753	$61.28	$61.30	$61.30
7 purchase totals =	$871.79		$953.9383	$953.94	$953.95	$953.90