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	$122.83	3.105%	$126.6439	$126.64	$126.65	$126.60
Purchase #2	$43.36	4.151%	$45.1599	$45.16	$45.15	$45.20
Purchase #3	$239.75	5.639%	$253.2695	$253.27	$253.25	$253.30
Purchase #4	$138.68	8.629%	$150.6467	$150.65	$150.65	$150.60
Purchase #5	$36.89	12.386%	$41.4592	$41.46	$41.45	$41.50
Purchase #6	$33.25	13.714%	$37.8099	$37.81	$37.80	$37.80
Purchase #7	$95.38	12.515%	$107.3168	$107.32	$107.30	$107.30
7 purchase totals =	$710.14		$762.3059	$762.31	$762.25	$762.30