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	$153.59	5.162%	$161.5183	$161.52	$161.50	$161.50
Purchase #2	$131.57	3.586%	$136.2881	$136.29	$136.30	$136.30
Purchase #3	$28.49	13.528%	$32.3441	$32.34	$32.35	$32.30
Purchase #4	$62.85	5.519%	$66.3187	$66.32	$66.30	$66.30
Purchase #5	$49.48	6.314%	$52.6042	$52.60	$52.60	$52.60
Purchase #6	$6.45	7.168%	$6.9123	$6.91	$6.90	$6.90
Purchase #7	$226.47	7.691%	$243.8878	$243.89	$243.90	$243.90
7 purchase totals =	$658.90		$699.8735	$699.87	$699.85	$699.80