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	$240.64	6.366%	$255.9591	$255.96	$255.95	$256.00
Purchase #2	$134.77	13.139%	$152.4774	$152.48	$152.50	$152.50
Purchase #3	$158.32	6.234%	$168.1897	$168.19	$168.20	$168.20
Purchase #4	$33.58	9.833%	$36.8819	$36.88	$36.90	$36.90
Purchase #5	$20.40	8.547%	$22.1436	$22.14	$22.15	$22.10
Purchase #6	$87.79	3.435%	$90.8056	$90.81	$90.80	$90.80
Purchase #7	$221.56	8.493%	$240.3771	$240.38	$240.40	$240.40
7 purchase totals =	$897.06		$966.8344	$966.84	$966.90	$966.90