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	$143.35	3.431%	$148.2683	$148.27	$148.25	$148.30
Purchase #2	$33.53	8.204%	$36.2808	$36.28	$36.30	$36.30
Purchase #3	$237.33	9.833%	$260.6667	$260.67	$260.65	$260.70
Purchase #4	$54.91	12.756%	$61.9143	$61.91	$61.90	$61.90
Purchase #5	$34.82	11.199%	$38.7195	$38.72	$38.70	$38.70
Purchase #6	$75.52	3.402%	$78.0892	$78.09	$78.10	$78.10
Purchase #7	$23.70	3.495%	$24.5283	$24.53	$24.55	$24.50
7 purchase totals =	$603.16		$648.4671	$648.47	$648.45	$648.50