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	$21.74	4.504%	$22.7192	$22.72	$22.70	$22.70
Purchase #2	$40.36	12.689%	$45.4813	$45.48	$45.50	$45.50
Purchase #3	$83.96	12.577%	$94.5196	$94.52	$94.50	$94.50
Purchase #4	$153.46	6.133%	$162.8717	$162.87	$162.85	$162.90
Purchase #5	$48.26	12.783%	$54.4291	$54.43	$54.45	$54.40
Purchase #6	$26.52	12.246%	$29.7676	$29.77	$29.75	$29.80
Purchase #7	$196.28	11.673%	$219.1918	$219.19	$219.20	$219.20
7 purchase totals =	$570.58		$628.9803	$628.98	$628.95	$629.00