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	$228.44	4.847%	$239.5125	$239.51	$239.50	$239.50
Purchase #2	$141.42	10.763%	$156.641	$156.64	$156.65	$156.60
Purchase #3	$87.34	4.223%	$91.0284	$91.03	$91.05	$91.00
Purchase #4	$209.92	6.151%	$222.8322	$222.83	$222.85	$222.80
Purchase #5	$137.68	4.249%	$143.53	$143.53	$143.55	$143.50
Purchase #6	$30.41	6.478%	$32.38	$32.38	$32.40	$32.40
Purchase #7	$35.38	3.344%	$36.5631	$36.56	$36.55	$36.60
7 purchase totals =	$870.59		$922.4872	$922.48	$922.55	$922.40