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	$52.49	6.231%	$55.7607	$55.76	$55.75	$55.80
Purchase #2	$83.53	11.214%	$92.8971	$92.90	$92.90	$92.90
Purchase #3	$61.57	8.672%	$66.9094	$66.91	$66.90	$66.90
Purchase #4	$164.89	5.211%	$173.4824	$173.48	$173.50	$173.50
Purchase #5	$117.92	8.448%	$127.8819	$127.88	$127.90	$127.90
Purchase #6	$153.39	12.702%	$172.8736	$172.87	$172.85	$172.90
Purchase #7	$70.58	4.733%	$73.9206	$73.92	$73.90	$73.90
7 purchase totals =	$704.37		$763.7257	$763.72	$763.70	$763.80