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	$107.32	4.823%	$112.496	$112.50	$112.50	$112.50
Purchase #2	$237.64	9.631%	$260.5271	$260.53	$260.55	$260.50
Purchase #3	$178.96	6.179%	$190.0179	$190.02	$190.00	$190.00
Purchase #4	$180.57	3.165%	$186.285	$186.29	$186.30	$186.30
Purchase #5	$175.38	8.734%	$190.6977	$190.70	$190.70	$190.70
Purchase #6	$120.50	6.715%	$128.5916	$128.59	$128.60	$128.60
Purchase #7	$39.56	10.795%	$43.8305	$43.83	$43.85	$43.80
7 purchase totals =	$1,039.93		$1,112.4458	$1,112.46	$1,112.50	$1,112.40