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 $48.83   4.397%   $50.9771   $50.98   $51.00   $51.00  
  Purchase #2 $184.70   4.858%   $193.6727   $193.67   $193.65   $193.70  
  Purchase #3 $23.38   13.418%   $26.5171   $26.52   $26.50   $26.50  
  Purchase #4 $77.64   10.652%   $85.9102   $85.91   $85.90   $85.90  
  Purchase #5 $69.76   12.439%   $78.4374   $78.44   $78.45   $78.40  
  Purchase #6 $165.72   8.861%   $180.4044   $180.40   $180.40   $180.40  
  Purchase #7 $32.41   4.557%   $33.8869   $33.89   $33.90   $33.90  
  7 purchase totals = $602.44       $649.8058   $649.81   $649.80   $649.80