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	$180.36	10.566%	$199.4168	$199.42	$199.40	$199.40
Purchase #2	$48.35	6.511%	$51.4981	$51.50	$51.50	$51.50
Purchase #3	$196.82	11.720%	$219.8873	$219.89	$219.90	$219.90
Purchase #4	$204.32	4.354%	$213.2161	$213.22	$213.20	$213.20
Purchase #5	$30.31	8.519%	$32.8921	$32.89	$32.90	$32.90
Purchase #6	$102.67	13.307%	$116.3323	$116.33	$116.35	$116.30
Purchase #7	$44.53	6.311%	$47.3403	$47.34	$47.35	$47.30
7 purchase totals =	$807.36		$880.5830	$880.59	$880.60	$880.50