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	$50.51	13.599%	$57.3789	$57.38	$57.40	$57.40
Purchase #2	$132.26	13.799%	$150.5106	$150.51	$150.50	$150.50
Purchase #3	$64.56	8.311%	$69.9256	$69.93	$69.95	$69.90
Purchase #4	$31.90	9.392%	$34.896	$34.90	$34.90	$34.90
Purchase #5	$43.48	3.571%	$45.0327	$45.03	$45.05	$45.00
Purchase #6	$91.73	12.834%	$103.5026	$103.50	$103.50	$103.50
Purchase #7	$86.43	6.149%	$91.7446	$91.74	$91.75	$91.70
7 purchase totals =	$500.87		$552.9910	$552.99	$553.05	$552.90