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	$83.76	9.186%	$91.4542	$91.45	$91.45	$91.50
Purchase #2	$170.64	9.824%	$187.4037	$187.40	$187.40	$187.40
Purchase #3	$24.81	12.600%	$27.9361	$27.94	$27.95	$27.90
Purchase #4	$243.81	13.652%	$277.0949	$277.09	$277.10	$277.10
Purchase #5	$238.40	7.762%	$256.9046	$256.90	$256.90	$256.90
Purchase #6	$42.77	11.143%	$47.5359	$47.54	$47.55	$47.50
Purchase #7	$211.51	9.455%	$231.5083	$231.51	$231.50	$231.50
7 purchase totals =	$1,015.70		$1,119.8377	$1,119.83	$1,119.85	$1,119.80