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	$42.90	12.600%	$48.3054	$48.31	$48.30	$48.30
Purchase #2	$137.71	12.520%	$154.9513	$154.95	$154.95	$155.00
Purchase #3	$167.43	11.715%	$187.0444	$187.04	$187.05	$187.00
Purchase #4	$58.61	12.534%	$65.9562	$65.96	$65.95	$66.00
Purchase #5	$78.63	11.216%	$87.4491	$87.45	$87.45	$87.40
Purchase #6	$102.84	5.573%	$108.5713	$108.57	$108.55	$108.60
Purchase #7	$88.59	13.546%	$100.5904	$100.59	$100.60	$100.60
7 purchase totals =	$676.71		$752.8681	$752.87	$752.85	$752.90