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	$122.74	8.759%	$133.4908	$133.49	$133.50	$133.50
Purchase #2	$32.93	4.849%	$34.5268	$34.53	$34.55	$34.50
Purchase #3	$36.50	8.175%	$39.4839	$39.48	$39.50	$39.50
Purchase #4	$174.32	13.725%	$198.2454	$198.25	$198.25	$198.20
Purchase #5	$133.59	13.333%	$151.4016	$151.40	$151.40	$151.40
Purchase #6	$149.31	12.642%	$168.1858	$168.19	$168.20	$168.20
Purchase #7	$225.66	13.155%	$255.3456	$255.35	$255.35	$255.30
7 purchase totals =	$875.05		$980.6799	$980.69	$980.75	$980.60