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	$94.59	8.750%	$102.8666	$102.87	$102.85	$102.90
Purchase #2	$85.34	4.143%	$88.8756	$88.88	$88.90	$88.90
Purchase #3	$160.54	13.696%	$182.5276	$182.53	$182.55	$182.50
Purchase #4	$167.38	13.713%	$190.3328	$190.33	$190.35	$190.30
Purchase #5	$97.69	3.183%	$100.7995	$100.80	$100.80	$100.80
Purchase #6	$37.48	8.680%	$40.7333	$40.73	$40.75	$40.70
Purchase #7	$121.71	9.648%	$133.4526	$133.45	$133.45	$133.50
7 purchase totals =	$764.73		$839.5880	$839.59	$839.65	$839.60