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 $188.53   13.514%   $214.0079   $214.01   $214.00   $214.00  
  Purchase #2 $24.59   5.221%   $25.8738   $25.87   $25.85   $25.90  
  Purchase #3 $187.37   3.464%   $193.8605   $193.86   $193.85   $193.90  
  Purchase #4 $7.27   3.229%   $7.5047   $7.50   $7.50   $7.50  
  Purchase #5 $117.99   11.540%   $131.606   $131.61   $131.60   $131.60  
  Purchase #6 $233.65   13.259%   $264.6297   $264.63   $264.65   $264.60  
  Purchase #7 $222.73   3.452%   $230.4186   $230.42   $230.40   $230.40  
  7 purchase totals = $982.13       $1,067.9012   $1,067.90   $1,067.85   $1,067.90