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 $136.77   9.276%   $149.4568   $149.46   $149.45   $149.50  
  Purchase #2 $244.80   8.840%   $266.4403   $266.44   $266.45   $266.40  
  Purchase #3 $237.29   8.685%   $257.8986   $257.90   $257.90   $257.90  
  Purchase #4 $17.96   5.159%   $18.8866   $18.89   $18.90   $18.90  
  Purchase #5 $68.92   4.357%   $71.9228   $71.92   $71.90   $71.90  
  Purchase #6 $207.67   7.681%   $223.6211   $223.62   $223.60   $223.60  
  Purchase #7 $23.71   7.871%   $25.5762   $25.58   $25.60   $25.60  
  7 purchase totals = $937.12       $1,013.8024   $1,013.81   $1,013.80   $1,013.80