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	$179.72	4.782%	$188.3142	$188.31	$188.30	$188.30
Purchase #2	$65.45	13.440%	$74.2465	$74.25	$74.25	$74.20
Purchase #3	$233.54	9.568%	$255.8851	$255.89	$255.90	$255.90
Purchase #4	$176.40	7.710%	$190.0004	$190.00	$190.00	$190.00
Purchase #5	$163.33	12.440%	$183.6483	$183.65	$183.65	$183.60
Purchase #6	$30.92	10.661%	$34.2164	$34.22	$34.20	$34.20
Purchase #7	$101.72	3.166%	$104.9405	$104.94	$104.95	$104.90
7 purchase totals =	$951.08		$1,031.2514	$1,031.26	$1,031.25	$1,031.10