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 $84.38   10.746%   $93.4475   $93.45   $93.45   $93.40  
  Purchase #2 $70.26   12.271%   $78.8816   $78.88   $78.90   $78.90  
  Purchase #3 $89.31   10.841%   $98.9921   $98.99   $99.00   $99.00  
  Purchase #4 $98.37   5.704%   $103.981   $103.98   $104.00   $104.00  
  Purchase #5 $127.71   6.165%   $135.5833   $135.58   $135.60   $135.60  
  Purchase #6 $243.50   12.473%   $273.8718   $273.87   $273.85   $273.90  
  Purchase #7 $168.69   7.866%   $181.9592   $181.96   $181.95   $182.00  
  7 purchase totals = $882.22       $966.7165   $966.71   $966.75   $966.80