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	$35.48	13.421%	$40.2418	$40.24	$40.25	$40.20
Purchase #2	$43.64	11.143%	$48.5028	$48.50	$48.50	$48.50
Purchase #3	$227.66	12.238%	$255.521	$255.52	$255.50	$255.50
Purchase #4	$77.45	7.744%	$83.4477	$83.45	$83.45	$83.40
Purchase #5	$162.51	7.265%	$174.3164	$174.32	$174.30	$174.30
Purchase #6	$174.38	9.103%	$190.2538	$190.25	$190.25	$190.30
Purchase #7	$131.47	13.610%	$149.3631	$149.36	$149.35	$149.40
7 purchase totals =	$852.59		$941.6466	$941.64	$941.60	$941.60