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	$60.78	9.480%	$66.5419	$66.54	$66.55	$66.50
Purchase #2	$179.72	3.647%	$186.2744	$186.27	$186.25	$186.30
Purchase #3	$55.85	7.219%	$59.8818	$59.88	$59.90	$59.90
Purchase #4	$22.26	9.534%	$24.3823	$24.38	$24.40	$24.40
Purchase #5	$136.37	6.286%	$144.9422	$144.94	$144.95	$144.90
Purchase #6	$232.67	6.540%	$247.8866	$247.89	$247.90	$247.90
Purchase #7	$123.33	8.386%	$133.6725	$133.67	$133.65	$133.70
7 purchase totals =	$810.98		$863.5817	$863.57	$863.60	$863.60