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	$5.48	6.269%	$5.8235	$5.82	$5.80	$5.80
Purchase #2	$202.85	11.545%	$226.269	$226.27	$226.25	$226.30
Purchase #3	$95.88	13.609%	$108.9283	$108.93	$108.95	$108.90
Purchase #4	$37.26	8.719%	$40.5087	$40.51	$40.50	$40.50
Purchase #5	$226.41	7.264%	$242.8564	$242.86	$242.85	$242.90
Purchase #6	$157.53	9.368%	$172.2874	$172.29	$172.30	$172.30
Purchase #7	$127.86	12.489%	$143.8284	$143.83	$143.85	$143.80
7 purchase totals =	$853.27		$940.5017	$940.51	$940.50	$940.50