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	$132.29	13.840%	$150.5989	$150.60	$150.60	$150.60
Purchase #2	$49.71	5.636%	$52.5117	$52.51	$52.50	$52.50
Purchase #3	$145.65	3.266%	$150.4069	$150.41	$150.40	$150.40
Purchase #4	$227.44	10.208%	$250.6571	$250.66	$250.65	$250.70
Purchase #5	$158.54	11.770%	$177.2002	$177.20	$177.20	$177.20
Purchase #6	$72.77	11.157%	$80.8889	$80.89	$80.90	$80.90
Purchase #7	$194.35	5.653%	$205.3366	$205.34	$205.35	$205.30
7 purchase totals =	$980.75		$1,067.6003	$1,067.61	$1,067.60	$1,067.60