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	$63.50	6.779%	$67.8047	$67.80	$67.80	$67.80
Purchase #2	$105.72	6.436%	$112.5241	$112.52	$112.50	$112.50
Purchase #3	$101.85	3.394%	$105.3068	$105.31	$105.30	$105.30
Purchase #4	$246.86	11.129%	$274.333	$274.33	$274.35	$274.30
Purchase #5	$23.71	13.296%	$26.8625	$26.86	$26.85	$26.90
Purchase #6	$155.41	4.246%	$162.0087	$162.01	$162.00	$162.00
Purchase #7	$85.72	9.713%	$94.046	$94.05	$94.05	$94.00
7 purchase totals =	$782.77		$842.8858	$842.88	$842.85	$842.80