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	$135.36	6.670%	$144.3885	$144.39	$144.40	$144.40
Purchase #2	$127.74	13.385%	$144.838	$144.84	$144.85	$144.80
Purchase #3	$189.72	9.873%	$208.4511	$208.45	$208.45	$208.50
Purchase #4	$176.94	3.393%	$182.9436	$182.94	$182.95	$182.90
Purchase #5	$197.97	12.337%	$222.3936	$222.39	$222.40	$222.40
Purchase #6	$86.39	6.713%	$92.1894	$92.19	$92.20	$92.20
Purchase #7	$118.52	7.605%	$127.5334	$127.53	$127.55	$127.50
7 purchase totals =	$1,032.64		$1,122.7376	$1,122.73	$1,122.80	$1,122.70