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	$35.47	4.782%	$37.1662	$37.17	$37.15	$37.20
Purchase #2	$131.46	9.801%	$144.3444	$144.34	$144.35	$144.30
Purchase #3	$109.39	12.321%	$122.8679	$122.87	$122.85	$122.90
Purchase #4	$213.52	9.598%	$234.0136	$234.01	$234.00	$234.00
Purchase #5	$160.26	7.353%	$172.0439	$172.04	$172.05	$172.00
Purchase #6	$103.44	10.692%	$114.4998	$114.50	$114.50	$114.50
Purchase #7	$160.84	4.872%	$168.6761	$168.68	$168.70	$168.70
7 purchase totals =	$914.38		$993.6119	$993.61	$993.60	$993.60