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	$92.78	9.474%	$101.57	$101.57	$101.55	$101.60
Purchase #2	$146.84	4.578%	$153.5623	$153.56	$153.55	$153.60
Purchase #3	$128.54	11.554%	$143.3915	$143.39	$143.40	$143.40
Purchase #4	$39.83	6.401%	$42.3795	$42.38	$42.40	$42.40
Purchase #5	$124.72	3.120%	$128.6113	$128.61	$128.60	$128.60
Purchase #6	$75.84	12.678%	$85.455	$85.46	$85.45	$85.50
Purchase #7	$243.98	8.753%	$265.3356	$265.34	$265.35	$265.30
7 purchase totals =	$852.53		$920.3052	$920.31	$920.30	$920.40