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	$100.40	4.779%	$105.1981	$105.20	$105.20	$105.20
Purchase #2	$171.59	11.252%	$190.8973	$190.90	$190.90	$190.90
Purchase #3	$153.62	9.309%	$167.9205	$167.92	$167.90	$167.90
Purchase #4	$206.85	12.130%	$231.9409	$231.94	$231.95	$231.90
Purchase #5	$85.72	5.285%	$90.2503	$90.25	$90.25	$90.30
Purchase #6	$22.71	11.765%	$25.3818	$25.38	$25.40	$25.40
Purchase #7	$176.42	5.649%	$186.386	$186.39	$186.40	$186.40
7 purchase totals =	$917.31		$997.9749	$997.98	$998.00	$998.00