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	$33.79	11.854%	$37.7955	$37.80	$37.80	$37.80
Purchase #2	$6.46	10.635%	$7.147	$7.15	$7.15	$7.10
Purchase #3	$213.32	5.782%	$225.6542	$225.65	$225.65	$225.70
Purchase #4	$41.39	11.158%	$46.0083	$46.01	$46.00	$46.00
Purchase #5	$45.89	8.871%	$49.9609	$49.96	$49.95	$50.00
Purchase #6	$85.72	11.471%	$95.5529	$95.55	$95.55	$95.60
Purchase #7	$132.78	8.388%	$143.9176	$143.92	$143.90	$143.90
7 purchase totals =	$559.35		$606.0364	$606.04	$606.00	$606.10