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	$167.89	13.535%	$190.6139	$190.61	$190.60	$190.60
Purchase #2	$83.66	6.835%	$89.3782	$89.38	$89.40	$89.40
Purchase #3	$155.45	13.299%	$176.1233	$176.12	$176.10	$176.10
Purchase #4	$222.87	12.810%	$251.4196	$251.42	$251.40	$251.40
Purchase #5	$144.56	6.337%	$153.7208	$153.72	$153.70	$153.70
Purchase #6	$13.70	12.693%	$15.4389	$15.44	$15.45	$15.40
Purchase #7	$117.62	8.185%	$127.2472	$127.25	$127.25	$127.20
7 purchase totals =	$905.75		$1,003.9419	$1,003.94	$1,003.90	$1,003.80