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	$60.88	5.824%	$64.4257	$64.43	$64.45	$64.40
Purchase #2	$161.37	7.274%	$173.1081	$173.11	$173.10	$173.10
Purchase #3	$95.68	8.132%	$103.4607	$103.46	$103.45	$103.50
Purchase #4	$247.96	8.189%	$268.2654	$268.27	$268.25	$268.30
Purchase #5	$212.66	8.575%	$230.8956	$230.90	$230.90	$230.90
Purchase #6	$60.44	12.335%	$67.8953	$67.90	$67.90	$67.90
Purchase #7	$123.65	6.615%	$131.8294	$131.83	$131.85	$131.80
7 purchase totals =	$962.64		$1,039.8802	$1,039.90	$1,039.90	$1,039.90