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	$130.82	9.143%	$142.7809	$142.78	$142.80	$142.80
Purchase #2	$201.98	12.685%	$227.6012	$227.60	$227.60	$227.60
Purchase #3	$150.68	3.339%	$155.7112	$155.71	$155.70	$155.70
Purchase #4	$116.83	7.854%	$126.0058	$126.01	$126.00	$126.00
Purchase #5	$16.50	12.244%	$18.5203	$18.52	$18.50	$18.50
Purchase #6	$162.49	10.336%	$179.285	$179.29	$179.30	$179.30
Purchase #7	$88.57	12.102%	$99.2887	$99.29	$99.30	$99.30
7 purchase totals =	$867.87		$949.1931	$949.20	$949.20	$949.20