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	$226.52	12.507%	$254.8509	$254.85	$254.85	$254.90
Purchase #2	$68.39	13.342%	$77.5146	$77.51	$77.50	$77.50
Purchase #3	$109.70	11.506%	$122.3221	$122.32	$122.30	$122.30
Purchase #4	$140.54	4.513%	$146.8826	$146.88	$146.90	$146.90
Purchase #5	$246.27	12.616%	$277.3394	$277.34	$277.35	$277.30
Purchase #6	$113.42	12.682%	$127.8039	$127.80	$127.80	$127.80
Purchase #7	$65.79	7.774%	$70.9045	$70.90	$70.90	$70.90
7 purchase totals =	$970.63		$1,077.6180	$1,077.60	$1,077.60	$1,077.60