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	$7.56	12.258%	$8.4867	$8.49	$8.50	$8.50
Purchase #2	$153.46	12.227%	$172.2236	$172.22	$172.20	$172.20
Purchase #3	$54.94	6.397%	$58.4545	$58.45	$58.45	$58.50
Purchase #4	$35.43	6.807%	$37.8417	$37.84	$37.85	$37.80
Purchase #5	$136.49	5.415%	$143.8809	$143.88	$143.90	$143.90
Purchase #6	$9.65	9.853%	$10.6008	$10.60	$10.60	$10.60
Purchase #7	$139.65	3.410%	$144.4121	$144.41	$144.40	$144.40
7 purchase totals =	$537.18		$575.9003	$575.89	$575.90	$575.90