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	$54.66	8.387%	$59.2443	$59.24	$59.25	$59.20
Purchase #2	$142.50	7.110%	$152.6318	$152.63	$152.65	$152.60
Purchase #3	$234.41	6.863%	$250.4976	$250.50	$250.50	$250.50
Purchase #4	$232.94	8.127%	$251.871	$251.87	$251.85	$251.90
Purchase #5	$38.95	6.395%	$41.4409	$41.44	$41.45	$41.40
Purchase #6	$52.31	13.264%	$59.2484	$59.25	$59.25	$59.20
Purchase #7	$78.51	12.182%	$88.0741	$88.07	$88.05	$88.10
7 purchase totals =	$834.28		$903.0081	$903.00	$903.00	$902.90