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 $244.63   11.269%   $272.1974   $272.20   $272.20   $272.20  
  Purchase #2 $12.34   11.840%   $13.8011   $13.80   $13.80   $13.80  
  Purchase #3 $165.65   5.193%   $174.2522   $174.25   $174.25   $174.30  
  Purchase #4 $53.34   12.249%   $59.8736   $59.87   $59.85   $59.90  
  Purchase #5 $78.60   3.212%   $81.1246   $81.12   $81.10   $81.10  
  Purchase #6 $46.53   4.636%   $48.6871   $48.69   $48.70   $48.70  
  Purchase #7 $32.89   9.441%   $35.9951   $36.00   $36.00   $36.00  
  7 purchase totals = $633.98       $685.9311   $685.93   $685.90   $686.00