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 $32.63   13.822%   $37.1401   $37.14   $37.15   $37.10  
  Purchase #2 $138.87   6.189%   $147.4647   $147.46   $147.45   $147.50  
  Purchase #3 $72.44   7.620%   $77.9599   $77.96   $77.95   $78.00  
  Purchase #4 $234.32   7.110%   $250.9802   $250.98   $251.00   $251.00  
  Purchase #5 $157.65   4.184%   $164.2461   $164.25   $164.25   $164.20  
  Purchase #6 $7.80   13.710%   $8.8694   $8.87   $8.85   $8.90  
  Purchase #7 $239.85   6.337%   $255.0493   $255.05   $255.05   $255.00  
  7 purchase totals = $883.56       $941.7097   $941.71   $941.70   $941.70