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	$248.69	13.382%	$281.9697	$281.97	$281.95	$282.00
Purchase #2	$200.78	3.803%	$208.4157	$208.42	$208.40	$208.40
Purchase #3	$61.73	11.164%	$68.6215	$68.62	$68.60	$68.60
Purchase #4	$123.48	7.151%	$132.3101	$132.31	$132.30	$132.30
Purchase #5	$35.61	13.656%	$40.4729	$40.47	$40.45	$40.50
Purchase #6	$37.76	6.750%	$40.3088	$40.31	$40.30	$40.30
Purchase #7	$14.56	3.147%	$15.0182	$15.02	$15.00	$15.00
7 purchase totals =	$722.61		$787.1169	$787.12	$787.00	$787.10