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	$226.31	13.521%	$256.9094	$256.91	$256.90	$256.90
Purchase #2	$54.58	12.606%	$61.4604	$61.46	$61.45	$61.50
Purchase #3	$21.55	4.224%	$22.4603	$22.46	$22.45	$22.50
Purchase #4	$155.70	13.729%	$177.0761	$177.08	$177.10	$177.10
Purchase #5	$30.48	12.668%	$34.3412	$34.34	$34.35	$34.30
Purchase #6	$167.79	13.567%	$190.5541	$190.55	$190.55	$190.60
Purchase #7	$176.89	7.465%	$190.0948	$190.09	$190.10	$190.10
7 purchase totals =	$833.30		$932.8963	$932.89	$932.90	$933.00