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	$29.56	5.116%	$31.0723	$31.07	$31.05	$31.10
Purchase #2	$38.85	9.153%	$42.4059	$42.41	$42.40	$42.40
Purchase #3	$151.85	11.851%	$169.8457	$169.85	$169.85	$169.80
Purchase #4	$123.97	10.566%	$137.0687	$137.07	$137.05	$137.10
Purchase #5	$93.56	7.160%	$100.2589	$100.26	$100.25	$100.30
Purchase #6	$241.80	13.660%	$274.8299	$274.83	$274.85	$274.80
Purchase #7	$241.66	10.396%	$266.783	$266.78	$266.80	$266.80
7 purchase totals =	$921.25		$1,022.2644	$1,022.27	$1,022.25	$1,022.30