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	$44.36	12.653%	$49.9729	$49.97	$49.95	$50.00
Purchase #2	$74.53	5.696%	$78.7752	$78.78	$78.80	$78.80
Purchase #3	$83.90	8.711%	$91.2085	$91.21	$91.20	$91.20
Purchase #4	$30.58	6.675%	$32.6212	$32.62	$32.60	$32.60
Purchase #5	$73.46	13.126%	$83.1024	$83.10	$83.10	$83.10
Purchase #6	$35.47	4.759%	$37.158	$37.16	$37.15	$37.20
Purchase #7	$85.93	11.633%	$95.9262	$95.93	$95.95	$95.90
7 purchase totals =	$428.23		$468.7644	$468.77	$468.75	$468.80