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	$140.52	3.404%	$145.3033	$145.30	$145.30	$145.30
Purchase #2	$220.74	13.207%	$249.8931	$249.89	$249.90	$249.90
Purchase #3	$170.94	5.105%	$179.6665	$179.67	$179.65	$179.70
Purchase #4	$172.66	8.263%	$186.9269	$186.93	$186.95	$186.90
Purchase #5	$10.83	13.686%	$12.3122	$12.31	$12.30	$12.30
Purchase #6	$198.81	9.140%	$216.9812	$216.98	$217.00	$217.00
Purchase #7	$113.53	12.541%	$127.7678	$127.77	$127.75	$127.80
7 purchase totals =	$1,028.03		$1,118.8510	$1,118.85	$1,118.85	$1,118.90