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 $76.39   11.357%   $85.0656   $85.07   $85.05   $85.10  
  Purchase #2 $45.84   6.305%   $48.7302   $48.73   $48.75   $48.70  
  Purchase #3 $113.97   10.189%   $125.5824   $125.58   $125.60   $125.60  
  Purchase #4 $37.28   9.744%   $40.9126   $40.91   $40.90   $40.90  
  Purchase #5 $191.65   3.569%   $198.49   $198.49   $198.50   $198.50  
  Purchase #6 $78.47   8.755%   $85.34   $85.34   $85.35   $85.30  
  Purchase #7 $171.70   6.797%   $183.3704   $183.37   $183.35   $183.40  
  7 purchase totals = $715.30       $767.4912   $767.49   $767.50   $767.50