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	$246.73	10.662%	$273.0364	$273.04	$273.05	$273.00
Purchase #2	$22.72	7.441%	$24.4106	$24.41	$24.40	$24.40
Purchase #3	$113.82	8.691%	$123.7121	$123.71	$123.70	$123.70
Purchase #4	$102.99	8.103%	$111.3353	$111.34	$111.35	$111.30
Purchase #5	$117.80	5.357%	$124.1105	$124.11	$124.10	$124.10
Purchase #6	$217.88	9.164%	$237.8465	$237.85	$237.85	$237.80
Purchase #7	$237.95	7.834%	$256.591	$256.59	$256.60	$256.60
7 purchase totals =	$1,059.89		$1,151.0424	$1,151.05	$1,151.05	$1,150.90