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	$148.91	5.694%	$157.3889	$157.39	$157.40	$157.40
Purchase #2	$138.26	8.718%	$150.3135	$150.31	$150.30	$150.30
Purchase #3	$68.94	12.119%	$77.2948	$77.29	$77.30	$77.30
Purchase #4	$167.66	7.391%	$180.0518	$180.05	$180.05	$180.10
Purchase #5	$98.50	13.639%	$111.9344	$111.93	$111.95	$111.90
Purchase #6	$182.86	9.105%	$199.5094	$199.51	$199.50	$199.50
Purchase #7	$83.25	11.241%	$92.6081	$92.61	$92.60	$92.60
7 purchase totals =	$888.38		$969.1009	$969.09	$969.10	$969.10