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	$221.94	7.459%	$238.4945	$238.49	$238.50	$238.50
Purchase #2	$55.46	6.761%	$59.2097	$59.21	$59.20	$59.20
Purchase #3	$153.93	13.208%	$174.2611	$174.26	$174.25	$174.30
Purchase #4	$66.76	11.118%	$74.1824	$74.18	$74.20	$74.20
Purchase #5	$76.85	13.850%	$87.4937	$87.49	$87.50	$87.50
Purchase #6	$81.77	9.548%	$89.5774	$89.58	$89.60	$89.60
Purchase #7	$143.63	6.728%	$153.2934	$153.29	$153.30	$153.30
7 purchase totals =	$800.34		$876.5122	$876.50	$876.55	$876.60