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	$59.84	6.248%	$63.5788	$63.58	$63.60	$63.60
Purchase #2	$26.94	5.700%	$28.4756	$28.48	$28.50	$28.50
Purchase #3	$215.46	11.199%	$239.5894	$239.59	$239.60	$239.60
Purchase #4	$168.68	10.177%	$185.8466	$185.85	$185.85	$185.80
Purchase #5	$225.33	7.407%	$242.0202	$242.02	$242.00	$242.00
Purchase #6	$17.48	11.496%	$19.4895	$19.49	$19.50	$19.50
Purchase #7	$185.83	7.854%	$200.4251	$200.43	$200.45	$200.40
7 purchase totals =	$899.56		$979.4252	$979.44	$979.50	$979.40