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	$117.78	12.630%	$132.6556	$132.66	$132.65	$132.70
Purchase #2	$84.83	5.240%	$89.2751	$89.28	$89.30	$89.30
Purchase #3	$176.85	10.360%	$195.1717	$195.17	$195.15	$195.20
Purchase #4	$83.28	13.527%	$94.5453	$94.55	$94.55	$94.50
Purchase #5	$37.38	7.596%	$40.2194	$40.22	$40.20	$40.20
Purchase #6	$24.77	4.644%	$25.9203	$25.92	$25.90	$25.90
Purchase #7	$60.34	10.143%	$66.4603	$66.46	$66.45	$66.50
7 purchase totals =	$585.23		$644.2477	$644.26	$644.20	$644.30