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 $200.64   13.608%   $227.9431   $227.94   $227.95   $227.90  
  Purchase #2 $242.47   13.288%   $274.6894   $274.69   $274.70   $274.70  
  Purchase #3 $24.39   8.269%   $26.4068   $26.41   $26.40   $26.40  
  Purchase #4 $209.92   8.435%   $227.6268   $227.63   $227.65   $227.60  
  Purchase #5 $140.66   8.376%   $152.4417   $152.44   $152.45   $152.40  
  Purchase #6 $53.31   5.279%   $56.1242   $56.12   $56.10   $56.10  
  Purchase #7 $241.67   5.693%   $255.4283   $255.43   $255.45   $255.40  
  7 purchase totals = $1,113.06       $1,220.6603   $1,220.66   $1,220.70   $1,220.50