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	$30.29	3.824%	$31.4483	$31.45	$31.45	$31.40
Purchase #2	$62.57	5.627%	$66.0908	$66.09	$66.10	$66.10
Purchase #3	$37.66	12.776%	$42.4714	$42.47	$42.45	$42.50
Purchase #4	$126.87	3.524%	$131.3409	$131.34	$131.35	$131.30
Purchase #5	$31.54	4.102%	$32.8338	$32.83	$32.85	$32.80
Purchase #6	$119.68	13.711%	$136.0893	$136.09	$136.10	$136.10
Purchase #7	$22.63	13.152%	$25.6063	$25.61	$25.60	$25.60
7 purchase totals =	$431.24		$465.8808	$465.88	$465.90	$465.80