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 $36.86   11.302%   $41.0259   $41.03   $41.05   $41.00  
  Purchase #2 $80.44   10.833%   $89.1541   $89.15   $89.15   $89.20  
  Purchase #3 $214.70   4.593%   $224.5612   $224.56   $224.55   $224.60  
  Purchase #4 $225.53   5.466%   $237.8575   $237.86   $237.85   $237.90  
  Purchase #5 $190.30   10.841%   $210.9304   $210.93   $210.95   $210.90  
  Purchase #6 $76.35   13.151%   $86.3908   $86.39   $86.40   $86.40  
  Purchase #7 $54.49   4.615%   $57.0047   $57.00   $57.00   $57.00  
  7 purchase totals = $878.67       $946.9246   $946.92   $946.95   $947.00