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	$203.42	12.776%	$229.4089	$229.41	$229.40	$229.40
Purchase #2	$137.59	10.180%	$151.5967	$151.60	$151.60	$151.60
Purchase #3	$28.25	13.329%	$32.0154	$32.02	$32.00	$32.00
Purchase #4	$12.65	4.760%	$13.2521	$13.25	$13.25	$13.30
Purchase #5	$229.36	11.234%	$255.1263	$255.13	$255.15	$255.10
Purchase #6	$85.47	3.750%	$88.6751	$88.68	$88.70	$88.70
Purchase #7	$134.49	13.721%	$152.9434	$152.94	$152.95	$152.90
7 purchase totals =	$831.23		$923.0179	$923.03	$923.05	$923.00