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	$168.32	13.186%	$190.5147	$190.51	$190.50	$190.50
Purchase #2	$220.83	4.833%	$231.5027	$231.50	$231.50	$231.50
Purchase #3	$5.94	10.158%	$6.5434	$6.54	$6.55	$6.50
Purchase #4	$33.93	13.175%	$38.4003	$38.40	$38.40	$38.40
Purchase #5	$133.31	4.412%	$139.1916	$139.19	$139.20	$139.20
Purchase #6	$138.59	3.106%	$142.8946	$142.89	$142.90	$142.90
Purchase #7	$97.87	11.214%	$108.8451	$108.85	$108.85	$108.80
7 purchase totals =	$798.79		$857.8924	$857.88	$857.90	$857.80