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	$223.49	5.250%	$235.2232	$235.22	$235.20	$235.20
Purchase #2	$37.88	12.163%	$42.4873	$42.49	$42.50	$42.50
Purchase #3	$196.67	13.689%	$223.5922	$223.59	$223.60	$223.60
Purchase #4	$89.85	3.178%	$92.7054	$92.71	$92.70	$92.70
Purchase #5	$244.52	11.744%	$273.2364	$273.24	$273.25	$273.20
Purchase #6	$40.47	10.405%	$44.6809	$44.68	$44.70	$44.70
Purchase #7	$75.34	8.783%	$81.9571	$81.96	$81.95	$82.00
7 purchase totals =	$908.22		$993.8825	$993.89	$993.90	$993.90