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 $59.37   10.191%   $65.4204   $65.42   $65.40   $65.40  
  Purchase #2 $33.68   13.325%   $38.1679   $38.17   $38.15   $38.20  
  Purchase #3 $164.43   3.794%   $170.6685   $170.67   $170.65   $170.70  
  Purchase #4 $245.26   10.808%   $271.7677   $271.77   $271.75   $271.80  
  Purchase #5 $242.58   7.797%   $261.494   $261.49   $261.50   $261.50  
  Purchase #6 $64.63   12.437%   $72.668   $72.67   $72.65   $72.70  
  Purchase #7 $222.81   6.424%   $237.1233   $237.12   $237.10   $237.10  
  7 purchase totals = $1,032.76       $1,117.3098   $1,117.31   $1,117.20   $1,117.40