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	$30.43	3.222%	$31.4105	$31.41	$31.40	$31.40
Purchase #2	$181.75	10.256%	$200.3903	$200.39	$200.40	$200.40
Purchase #3	$111.67	4.196%	$116.3557	$116.36	$116.35	$116.40
Purchase #4	$222.82	10.470%	$246.1493	$246.15	$246.15	$246.10
Purchase #5	$43.90	9.362%	$48.0099	$48.01	$48.00	$48.00
Purchase #6	$75.96	7.793%	$81.8796	$81.88	$81.90	$81.90
Purchase #7	$37.85	10.620%	$41.8697	$41.87	$41.85	$41.90
7 purchase totals =	$704.38		$766.0650	$766.07	$766.05	$766.10