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 $246.50   3.732%   $255.6994   $255.70   $255.70   $255.70  
  Purchase #2 $245.77   11.371%   $273.7165   $273.72   $273.70   $273.70  
  Purchase #3 $182.66   4.433%   $190.7573   $190.76   $190.75   $190.80  
  Purchase #4 $62.29   7.206%   $66.7786   $66.78   $66.80   $66.80  
  Purchase #5 $26.49   13.439%   $30.05   $30.05   $30.05   $30.10  
  Purchase #6 $27.32   3.865%   $28.3759   $28.38   $28.40   $28.40  
  Purchase #7 $151.36   7.168%   $162.2095   $162.21   $162.20   $162.20  
  7 purchase totals = $942.39       $1,007.5872   $1,007.60   $1,007.60   $1,007.70