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	$124.68	12.431%	$140.179	$140.18	$140.20	$140.20
Purchase #2	$95.88	7.194%	$102.7776	$102.78	$102.80	$102.80
Purchase #3	$238.43	5.497%	$251.5365	$251.54	$251.55	$251.50
Purchase #4	$52.68	12.774%	$59.4093	$59.41	$59.40	$59.40
Purchase #5	$140.85	5.424%	$148.4897	$148.49	$148.50	$148.50
Purchase #6	$37.83	4.716%	$39.6141	$39.61	$39.60	$39.60
Purchase #7	$208.87	10.871%	$231.5763	$231.58	$231.60	$231.60
7 purchase totals =	$899.22		$973.5825	$973.59	$973.65	$973.60