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	$33.44	13.335%	$37.8992	$37.90	$37.90	$37.90
Purchase #2	$89.82	10.226%	$99.005	$99.01	$99.00	$99.00
Purchase #3	$233.49	9.579%	$255.856	$255.86	$255.85	$255.90
Purchase #4	$116.76	9.518%	$127.8732	$127.87	$127.85	$127.90
Purchase #5	$160.97	12.409%	$180.9448	$180.94	$180.95	$180.90
Purchase #6	$33.55	5.796%	$35.4946	$35.49	$35.50	$35.50
Purchase #7	$133.78	9.616%	$146.6443	$146.64	$146.65	$146.60
7 purchase totals =	$801.81		$883.7171	$883.71	$883.70	$883.70