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	$102.54	8.767%	$111.5297	$111.53	$111.55	$111.50
Purchase #2	$213.60	10.709%	$236.4744	$236.47	$236.45	$236.50
Purchase #3	$143.37	13.392%	$162.5701	$162.57	$162.55	$162.60
Purchase #4	$37.90	10.851%	$42.0125	$42.01	$42.00	$42.00
Purchase #5	$169.57	10.223%	$186.9051	$186.91	$186.90	$186.90
Purchase #6	$19.54	11.182%	$21.725	$21.73	$21.75	$21.70
Purchase #7	$35.82	4.292%	$37.3574	$37.36	$37.35	$37.40
7 purchase totals =	$722.34		$798.5742	$798.58	$798.55	$798.60