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	$214.45	11.545%	$239.2083	$239.21	$239.20	$239.20
Purchase #2	$33.43	13.113%	$37.8137	$37.81	$37.80	$37.80
Purchase #3	$75.92	12.279%	$85.2422	$85.24	$85.25	$85.20
Purchase #4	$247.95	3.236%	$255.9737	$255.97	$255.95	$256.00
Purchase #5	$87.67	5.625%	$92.6014	$92.60	$92.60	$92.60
Purchase #6	$114.56	11.611%	$127.8616	$127.86	$127.85	$127.90
Purchase #7	$78.51	5.295%	$82.6671	$82.67	$82.65	$82.70
7 purchase totals =	$852.49		$921.3680	$921.36	$921.30	$921.40