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	$179.73	6.208%	$190.8876	$190.89	$190.90	$190.90
Purchase #2	$199.52	10.434%	$220.3379	$220.34	$220.35	$220.30
Purchase #3	$26.87	3.452%	$27.7976	$27.80	$27.80	$27.80
Purchase #4	$217.41	11.715%	$242.8796	$242.88	$242.90	$242.90
Purchase #5	$38.86	10.833%	$43.0697	$43.07	$43.05	$43.10
Purchase #6	$32.43	7.576%	$34.8869	$34.89	$34.90	$34.90
Purchase #7	$83.28	5.200%	$87.6106	$87.61	$87.60	$87.60
7 purchase totals =	$778.10		$847.4699	$847.48	$847.50	$847.50