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	$45.83	7.509%	$49.2714	$49.27	$49.25	$49.30
Purchase #2	$113.54	12.581%	$127.8245	$127.82	$127.80	$127.80
Purchase #3	$157.51	10.854%	$174.6061	$174.61	$174.60	$174.60
Purchase #4	$104.87	8.145%	$113.4117	$113.41	$113.40	$113.40
Purchase #5	$102.51	6.862%	$109.5442	$109.54	$109.55	$109.50
Purchase #6	$222.85	10.440%	$246.1155	$246.12	$246.10	$246.10
Purchase #7	$153.36	10.162%	$168.9444	$168.94	$168.95	$168.90
7 purchase totals =	$900.47		$989.7178	$989.71	$989.65	$989.60