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 $31.29   6.633%   $33.3655   $33.37   $33.35   $33.40  
  Purchase #2 $222.42   9.537%   $243.6322   $243.63   $243.65   $243.60  
  Purchase #3 $81.68   5.257%   $85.9739   $85.97   $85.95   $86.00  
  Purchase #4 $138.41   5.845%   $146.5001   $146.50   $146.50   $146.50  
  Purchase #5 $23.26   11.235%   $25.8733   $25.87   $25.85   $25.90  
  Purchase #6 $169.45   9.765%   $185.9968   $186.00   $186.00   $186.00  
  Purchase #7 $89.66   4.766%   $93.9332   $93.93   $93.95   $93.90  
  7 purchase totals = $756.17       $815.2750   $815.27   $815.25   $815.30