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	$18.85	10.490%	$20.8274	$20.83	$20.85	$20.80
Purchase #2	$30.94	7.154%	$33.1534	$33.15	$33.15	$33.20
Purchase #3	$35.80	4.694%	$37.4805	$37.48	$37.50	$37.50
Purchase #4	$61.47	9.332%	$67.2064	$67.21	$67.20	$67.20
Purchase #5	$83.43	9.456%	$91.3191	$91.32	$91.30	$91.30
Purchase #6	$88.97	7.768%	$95.8812	$95.88	$95.90	$95.90
Purchase #7	$216.57	7.410%	$232.6178	$232.62	$232.60	$232.60
7 purchase totals =	$536.03		$578.4858	$578.49	$578.50	$578.50