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	$125.81	5.484%	$132.7094	$132.71	$132.70	$132.70
Purchase #2	$129.87	9.260%	$141.896	$141.90	$141.90	$141.90
Purchase #3	$110.30	5.795%	$116.6919	$116.69	$116.70	$116.70
Purchase #4	$221.99	12.170%	$249.0062	$249.01	$249.00	$249.00
Purchase #5	$34.57	8.722%	$37.5852	$37.59	$37.60	$37.60
Purchase #6	$104.74	6.298%	$111.3365	$111.34	$111.35	$111.30
Purchase #7	$35.32	8.847%	$38.4448	$38.44	$38.45	$38.40
7 purchase totals =	$762.60		$827.6700	$827.68	$827.70	$827.60