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	$37.98	6.691%	$40.5212	$40.52	$40.50	$40.50
Purchase #2	$34.35	5.579%	$36.2664	$36.27	$36.25	$36.30
Purchase #3	$198.88	11.252%	$221.258	$221.26	$221.25	$221.30
Purchase #4	$91.81	10.217%	$101.1902	$101.19	$101.20	$101.20
Purchase #5	$104.59	13.240%	$118.4377	$118.44	$118.45	$118.40
Purchase #6	$55.27	11.432%	$61.5885	$61.59	$61.60	$61.60
Purchase #7	$101.46	3.365%	$104.8741	$104.87	$104.85	$104.90
7 purchase totals =	$624.34		$684.1361	$684.14	$684.10	$684.20