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	$225.36	7.336%	$241.8924	$241.89	$241.90	$241.90
Purchase #2	$76.27	8.796%	$82.9787	$82.98	$83.00	$83.00
Purchase #3	$63.97	6.132%	$67.8926	$67.89	$67.90	$67.90
Purchase #4	$32.89	9.664%	$36.0685	$36.07	$36.05	$36.10
Purchase #5	$12.27	4.826%	$12.8622	$12.86	$12.85	$12.90
Purchase #6	$24.95	12.265%	$28.0101	$28.01	$28.00	$28.00
Purchase #7	$34.85	8.454%	$37.7962	$37.80	$37.80	$37.80
7 purchase totals =	$470.56		$507.5007	$507.50	$507.50	$507.60