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	$80.78	3.379%	$83.5096	$83.51	$83.50	$83.50
Purchase #2	$66.64	8.756%	$72.475	$72.48	$72.50	$72.50
Purchase #3	$164.94	8.495%	$178.9517	$178.95	$178.95	$179.00
Purchase #4	$157.29	9.134%	$171.6569	$171.66	$171.65	$171.70
Purchase #5	$15.48	13.478%	$17.5664	$17.57	$17.55	$17.60
Purchase #6	$5.86	12.146%	$6.5718	$6.57	$6.55	$6.60
Purchase #7	$244.95	10.436%	$270.513	$270.51	$270.50	$270.50
7 purchase totals =	$735.94		$801.2444	$801.25	$801.20	$801.40