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 $58.51   13.508%   $66.4135   $66.41   $66.40   $66.40  
  Purchase #2 $163.77   6.187%   $173.9024   $173.90   $173.90   $173.90  
  Purchase #3 $243.83   6.238%   $259.0401   $259.04   $259.05   $259.00  
  Purchase #4 $129.65   9.497%   $141.9629   $141.96   $141.95   $142.00  
  Purchase #5 $49.45   13.130%   $55.9428   $55.94   $55.95   $55.90  
  Purchase #6 $59.69   7.187%   $63.9799   $63.98   $64.00   $64.00  
  Purchase #7 $172.27   12.265%   $193.3989   $193.40   $193.40   $193.40  
  7 purchase totals = $877.17       $954.6405   $954.63   $954.65   $954.60