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 $179.44   11.307%   $199.7293   $199.73   $199.75   $199.70  
  Purchase #2 $240.75   4.189%   $250.835   $250.84   $250.85   $250.80  
  Purchase #3 $245.49   8.602%   $266.607   $266.61   $266.60   $266.60  
  Purchase #4 $88.29   3.149%   $91.0703   $91.07   $91.05   $91.10  
  Purchase #5 $94.95   9.604%   $104.069   $104.07   $104.05   $104.10  
  Purchase #6 $215.49   6.828%   $230.2037   $230.20   $230.20   $230.20  
  Purchase #7 $79.30   13.134%   $89.7153   $89.72   $89.70   $89.70  
  7 purchase totals = $1,143.71       $1,232.2296   $1,232.24   $1,232.20   $1,232.20