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	$245.65	12.708%	$276.8672	$276.87	$276.85	$276.90
Purchase #2	$162.48	6.376%	$172.8397	$172.84	$172.85	$172.80
Purchase #3	$47.50	4.395%	$49.5876	$49.59	$49.60	$49.60
Purchase #4	$150.55	4.246%	$156.9424	$156.94	$156.95	$156.90
Purchase #5	$228.93	4.274%	$238.7145	$238.71	$238.70	$238.70
Purchase #6	$88.47	12.249%	$99.3067	$99.31	$99.30	$99.30
Purchase #7	$246.30	10.843%	$273.0063	$273.01	$273.00	$273.00
7 purchase totals =	$1,169.88		$1,267.2644	$1,267.27	$1,267.25	$1,267.20