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	$106.74	8.761%	$116.0915	$116.09	$116.10	$116.10
Purchase #2	$36.65	7.329%	$39.3361	$39.34	$39.35	$39.30
Purchase #3	$147.95	8.763%	$160.9149	$160.91	$160.90	$160.90
Purchase #4	$89.39	12.824%	$100.8534	$100.85	$100.85	$100.90
Purchase #5	$38.60	5.572%	$40.7508	$40.75	$40.75	$40.80
Purchase #6	$107.38	10.400%	$118.5475	$118.55	$118.55	$118.50
Purchase #7	$140.43	5.632%	$148.339	$148.34	$148.35	$148.30
7 purchase totals =	$667.14		$724.8332	$724.83	$724.85	$724.80