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	$164.69	3.763%	$170.8873	$170.89	$170.90	$170.90
Purchase #2	$131.47	13.202%	$148.8267	$148.83	$148.85	$148.80
Purchase #3	$219.43	9.213%	$239.6461	$239.65	$239.65	$239.60
Purchase #4	$199.75	13.500%	$226.7163	$226.72	$226.70	$226.70
Purchase #5	$162.61	5.123%	$170.9405	$170.94	$170.95	$170.90
Purchase #6	$96.53	9.700%	$105.8934	$105.89	$105.90	$105.90
Purchase #7	$195.48	13.830%	$222.5149	$222.51	$222.50	$222.50
7 purchase totals =	$1,169.96		$1,285.4252	$1,285.43	$1,285.45	$1,285.30