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	$116.59	12.786%	$131.4972	$131.50	$131.50	$131.50
Purchase #2	$40.70	4.297%	$42.4489	$42.45	$42.45	$42.40
Purchase #3	$183.31	9.427%	$200.5906	$200.59	$200.60	$200.60
Purchase #4	$114.44	7.481%	$123.0013	$123.00	$123.00	$123.00
Purchase #5	$76.83	8.722%	$83.5311	$83.53	$83.55	$83.50
Purchase #6	$114.74	9.682%	$125.8491	$125.85	$125.85	$125.80
Purchase #7	$163.40	11.310%	$181.8805	$181.88	$181.90	$181.90
7 purchase totals =	$810.01		$888.7987	$888.80	$888.85	$888.70