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	$104.57	4.446%	$109.2192	$109.22	$109.20	$109.20
Purchase #2	$131.50	9.857%	$144.462	$144.46	$144.45	$144.50
Purchase #3	$48.67	12.589%	$54.7971	$54.80	$54.80	$54.80
Purchase #4	$132.95	4.121%	$138.4289	$138.43	$138.45	$138.40
Purchase #5	$82.98	9.156%	$90.5776	$90.58	$90.60	$90.60
Purchase #6	$33.75	11.244%	$37.5449	$37.54	$37.55	$37.50
Purchase #7	$222.54	4.548%	$232.6611	$232.66	$232.65	$232.70
7 purchase totals =	$756.96		$807.6908	$807.69	$807.70	$807.70