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 $24.33   8.360%   $26.364   $26.36   $26.35   $26.40  
  Purchase #2 $92.75   3.156%   $95.6772   $95.68   $95.70   $95.70  
  Purchase #3 $120.87   7.788%   $130.2834   $130.28   $130.30   $130.30  
  Purchase #4 $168.63   3.145%   $173.9334   $173.93   $173.95   $173.90  
  Purchase #5 $242.46   3.387%   $250.6721   $250.67   $250.65   $250.70  
  Purchase #6 $50.74   6.756%   $54.168   $54.17   $54.15   $54.20  
  Purchase #7 $64.87   7.866%   $69.9727   $69.97   $69.95   $70.00  
  7 purchase totals = $764.65       $801.0708   $801.06   $801.05   $801.20