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 $174.97   13.296%   $198.234   $198.23   $198.25   $198.20  
  Purchase #2 $121.39   9.798%   $133.2838   $133.28   $133.30   $133.30  
  Purchase #3 $186.81   6.782%   $199.4795   $199.48   $199.50   $199.50  
  Purchase #4 $60.48   6.675%   $64.517   $64.52   $64.50   $64.50  
  Purchase #5 $125.91   4.295%   $131.3178   $131.32   $131.30   $131.30  
  Purchase #6 $44.30   7.645%   $47.6867   $47.69   $47.70   $47.70  
  Purchase #7 $232.30   10.861%   $257.5301   $257.53   $257.55   $257.50  
  7 purchase totals = $946.16       $1,032.0489   $1,032.05   $1,032.10   $1,032.00