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 $150.28   8.249%   $162.6766   $162.68   $162.70   $162.70  
  Purchase #2 $61.56   13.815%   $70.0645   $70.06   $70.05   $70.10  
  Purchase #3 $62.62   10.748%   $69.3504   $69.35   $69.35   $69.40  
  Purchase #4 $193.59   5.669%   $204.5646   $204.56   $204.55   $204.60  
  Purchase #5 $115.63   8.591%   $125.5638   $125.56   $125.55   $125.60  
  Purchase #6 $225.87   13.838%   $257.1259   $257.13   $257.15   $257.10  
  Purchase #7 $61.44   4.327%   $64.0985   $64.10   $64.10   $64.10  
  7 purchase totals = $870.99       $953.4443   $953.44   $953.45   $953.60