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	$166.40	12.134%	$186.591	$186.59	$186.60	$186.60
Purchase #2	$230.74	5.584%	$243.6245	$243.62	$243.60	$243.60
Purchase #3	$176.28	8.110%	$190.5763	$190.58	$190.60	$190.60
Purchase #4	$161.67	5.470%	$170.5133	$170.51	$170.50	$170.50
Purchase #5	$208.63	6.688%	$222.5832	$222.58	$222.60	$222.60
Purchase #6	$205.48	13.842%	$233.9225	$233.92	$233.90	$233.90
Purchase #7	$239.25	6.643%	$255.1434	$255.14	$255.15	$255.10
7 purchase totals =	$1,388.45		$1,502.9542	$1,502.94	$1,502.95	$1,502.90