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	$68.81	5.128%	$72.3386	$72.34	$72.35	$72.30
Purchase #2	$229.67	13.601%	$260.9074	$260.91	$260.90	$260.90
Purchase #3	$196.40	12.126%	$220.2155	$220.22	$220.20	$220.20
Purchase #4	$7.83	10.870%	$8.6811	$8.68	$8.70	$8.70
Purchase #5	$83.66	8.287%	$90.5929	$90.59	$90.60	$90.60
Purchase #6	$135.85	3.669%	$140.8343	$140.83	$140.85	$140.80
Purchase #7	$78.90	10.455%	$87.149	$87.15	$87.15	$87.10
7 purchase totals =	$801.12		$880.7188	$880.72	$880.75	$880.60