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 $52.71   6.811%   $56.3001   $56.30   $56.30   $56.30  
  Purchase #2 $233.42   5.687%   $246.6946   $246.69   $246.70   $246.70  
  Purchase #3 $52.68   9.865%   $57.8769   $57.88   $57.90   $57.90  
  Purchase #4 $130.70   10.737%   $144.7333   $144.73   $144.75   $144.70  
  Purchase #5 $239.57   9.143%   $261.4739   $261.47   $261.45   $261.50  
  Purchase #6 $62.31   13.204%   $70.5374   $70.54   $70.55   $70.50  
  Purchase #7 $183.30   9.552%   $200.8088   $200.81   $200.80   $200.80  
  7 purchase totals = $954.69       $1,038.4250   $1,038.42   $1,038.45   $1,038.40