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 $195.99   8.471%   $212.5923   $212.59   $212.60   $212.60  
  Purchase #2 $236.45   9.835%   $259.7049   $259.70   $259.70   $259.70  
  Purchase #3 $76.48   7.735%   $82.3957   $82.40   $82.40   $82.40  
  Purchase #4 $197.45   8.874%   $214.9717   $214.97   $214.95   $215.00  
  Purchase #5 $33.97   3.623%   $35.2007   $35.20   $35.20   $35.20  
  Purchase #6 $242.32   6.690%   $258.5312   $258.53   $258.55   $258.50  
  Purchase #7 $170.27   13.544%   $193.3314   $193.33   $193.35   $193.30  
  7 purchase totals = $1,152.93       $1,256.7279   $1,256.72   $1,256.75   $1,256.70