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	$111.50	10.467%	$123.1707	$123.17	$123.15	$123.20
Purchase #2	$157.97	8.311%	$171.0989	$171.10	$171.10	$171.10
Purchase #3	$54.36	12.671%	$61.248	$61.25	$61.25	$61.20
Purchase #4	$101.26	3.168%	$104.4679	$104.47	$104.45	$104.50
Purchase #5	$208.90	8.843%	$227.373	$227.37	$227.35	$227.40
Purchase #6	$36.60	12.264%	$41.0886	$41.09	$41.10	$41.10
Purchase #7	$122.45	13.794%	$139.3408	$139.34	$139.35	$139.30
7 purchase totals =	$793.04		$867.7879	$867.79	$867.75	$867.80