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	$7.63	11.347%	$8.4958	$8.50	$8.50	$8.50
Purchase #2	$140.71	7.110%	$150.7145	$150.71	$150.70	$150.70
Purchase #3	$62.36	8.772%	$67.8302	$67.83	$67.85	$67.80
Purchase #4	$172.89	6.179%	$183.5729	$183.57	$183.55	$183.60
Purchase #5	$58.60	13.584%	$66.5602	$66.56	$66.55	$66.60
Purchase #6	$176.39	3.691%	$182.9006	$182.90	$182.90	$182.90
Purchase #7	$34.29	13.226%	$38.8252	$38.83	$38.85	$38.80
7 purchase totals =	$652.87		$698.8994	$698.90	$698.90	$698.90