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 $92.33   6.357%   $98.1994   $98.20   $98.20   $98.20  
  Purchase #2 $237.45   6.281%   $252.3642   $252.36   $252.35   $252.40  
  Purchase #3 $8.77   12.849%   $9.8969   $9.90   $9.90   $9.90  
  Purchase #4 $78.27   10.379%   $86.3936   $86.39   $86.40   $86.40  
  Purchase #5 $221.81   10.769%   $245.6967   $245.70   $245.70   $245.70  
  Purchase #6 $237.41   5.589%   $250.6788   $250.68   $250.70   $250.70  
  Purchase #7 $233.92   11.173%   $260.0559   $260.06   $260.05   $260.10  
  7 purchase totals = $1,109.96       $1,203.2855   $1,203.29   $1,203.30   $1,203.40