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	$71.88	13.249%	$81.4034	$81.40	$81.40	$81.40
Purchase #2	$203.53	13.710%	$231.434	$231.43	$231.45	$231.40
Purchase #3	$32.74	12.217%	$36.7398	$36.74	$36.75	$36.70
Purchase #4	$46.66	12.575%	$52.5275	$52.53	$52.55	$52.50
Purchase #5	$40.93	13.133%	$46.3053	$46.31	$46.30	$46.30
Purchase #6	$82.54	8.353%	$89.4346	$89.43	$89.45	$89.40
Purchase #7	$89.92	3.845%	$93.3774	$93.38	$93.40	$93.40
7 purchase totals =	$568.20		$631.2220	$631.22	$631.30	$631.10