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 $244.58   6.366%   $260.15   $260.15   $260.15   $260.20  
  Purchase #2 $129.35   5.821%   $136.8795   $136.88   $136.90   $136.90  
  Purchase #3 $77.81   6.839%   $83.1314   $83.13   $83.15   $83.10  
  Purchase #4 $234.25   12.319%   $263.1073   $263.11   $263.10   $263.10  
  Purchase #5 $162.75   12.213%   $182.6267   $182.63   $182.65   $182.60  
  Purchase #6 $33.90   3.584%   $35.115   $35.12   $35.10   $35.10  
  Purchase #7 $72.46   12.542%   $81.5479   $81.55   $81.55   $81.50  
  7 purchase totals = $955.10       $1,042.5578   $1,042.57   $1,042.60   $1,042.50