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	$242.50	8.796%	$263.8303	$263.83	$263.85	$263.80
Purchase #2	$95.38	12.666%	$107.4608	$107.46	$107.45	$107.50
Purchase #3	$65.72	9.787%	$72.152	$72.15	$72.15	$72.20
Purchase #4	$78.48	13.182%	$88.8252	$88.83	$88.85	$88.80
Purchase #5	$24.78	11.513%	$27.6329	$27.63	$27.65	$27.60
Purchase #6	$100.97	8.440%	$109.4919	$109.49	$109.50	$109.50
Purchase #7	$236.61	3.442%	$244.7541	$244.75	$244.75	$244.80
7 purchase totals =	$844.44		$914.1472	$914.14	$914.20	$914.20