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	$158.39	7.308%	$169.9651	$169.97	$169.95	$170.00
Purchase #2	$80.95	7.154%	$86.7412	$86.74	$86.75	$86.70
Purchase #3	$162.43	8.862%	$176.8245	$176.82	$176.80	$176.80
Purchase #4	$60.34	9.474%	$66.0566	$66.06	$66.05	$66.10
Purchase #5	$87.46	3.565%	$90.5779	$90.58	$90.60	$90.60
Purchase #6	$154.46	8.714%	$167.9196	$167.92	$167.90	$167.90
Purchase #7	$64.52	5.141%	$67.837	$67.84	$67.85	$67.80
7 purchase totals =	$768.55		$825.9219	$825.93	$825.90	$825.90