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	$59.71	11.408%	$66.5217	$66.52	$66.50	$66.50
Purchase #2	$139.78	3.347%	$144.4584	$144.46	$144.45	$144.50
Purchase #3	$146.51	11.181%	$162.8913	$162.89	$162.90	$162.90
Purchase #4	$64.86	7.710%	$69.8607	$69.86	$69.85	$69.90
Purchase #5	$239.77	8.787%	$260.8386	$260.84	$260.85	$260.80
Purchase #6	$178.61	4.534%	$186.7082	$186.71	$186.70	$186.70
Purchase #7	$40.41	6.743%	$43.1348	$43.13	$43.15	$43.10
7 purchase totals =	$869.65		$934.4137	$934.41	$934.40	$934.40