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	$136.67	4.334%	$142.5933	$142.59	$142.60	$142.60
Purchase #2	$12.53	7.663%	$13.4902	$13.49	$13.50	$13.50
Purchase #3	$119.85	9.766%	$131.5546	$131.55	$131.55	$131.60
Purchase #4	$35.84	13.123%	$40.5433	$40.54	$40.55	$40.50
Purchase #5	$177.56	7.198%	$190.3408	$190.34	$190.35	$190.30
Purchase #6	$117.32	11.504%	$130.8165	$130.82	$130.80	$130.80
Purchase #7	$58.33	13.561%	$66.2401	$66.24	$66.25	$66.20
7 purchase totals =	$658.10		$715.5788	$715.57	$715.60	$715.50