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	$98.26	9.429%	$107.5249	$107.52	$107.50	$107.50
Purchase #2	$112.89	9.369%	$123.4667	$123.47	$123.45	$123.50
Purchase #3	$152.68	3.494%	$158.0146	$158.01	$158.00	$158.00
Purchase #4	$27.25	7.868%	$29.394	$29.39	$29.40	$29.40
Purchase #5	$61.33	8.411%	$66.4885	$66.49	$66.50	$66.50
Purchase #6	$95.93	4.135%	$99.8967	$99.90	$99.90	$99.90
Purchase #7	$230.56	4.558%	$241.0689	$241.07	$241.05	$241.10
7 purchase totals =	$778.90		$825.8543	$825.85	$825.80	$825.90