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	$131.75	12.807%	$148.6232	$148.62	$148.60	$148.60
Purchase #2	$32.65	9.264%	$35.6747	$35.67	$35.65	$35.70
Purchase #3	$51.65	5.336%	$54.406	$54.41	$54.40	$54.40
Purchase #4	$35.85	11.147%	$39.8462	$39.85	$39.85	$39.80
Purchase #5	$33.26	13.619%	$37.7897	$37.79	$37.80	$37.80
Purchase #6	$127.77	9.360%	$139.7293	$139.73	$139.75	$139.70
Purchase #7	$78.26	7.178%	$83.8775	$83.88	$83.90	$83.90
7 purchase totals =	$491.19		$539.9466	$539.95	$539.95	$539.90