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 $66.42   13.868%   $75.6311   $75.63   $75.65   $75.60  
  Purchase #2 $101.39   8.374%   $109.8804   $109.88   $109.90   $109.90  
  Purchase #3 $214.43   10.867%   $237.7321   $237.73   $237.75   $237.70  
  Purchase #4 $216.54   11.854%   $242.2087   $242.21   $242.20   $242.20  
  Purchase #5 $88.44   12.832%   $99.7886   $99.79   $99.80   $99.80  
  Purchase #6 $201.42   13.166%   $227.939   $227.94   $227.95   $227.90  
  Purchase #7 $17.33   6.322%   $18.4256   $18.43   $18.45   $18.40  
  7 purchase totals = $905.97       $1,011.6055   $1,011.61   $1,011.70   $1,011.50