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 $120.26   13.826%   $136.8871   $136.89   $136.90   $136.90  
  Purchase #2 $214.67   12.339%   $241.1581   $241.16   $241.15   $241.20  
  Purchase #3 $187.86   10.709%   $207.9779   $207.98   $208.00   $208.00  
  Purchase #4 $159.29   13.569%   $180.9041   $180.90   $180.90   $180.90  
  Purchase #5 $109.36   11.828%   $122.2951   $122.30   $122.30   $122.30  
  Purchase #6 $15.92   7.426%   $17.1022   $17.10   $17.10   $17.10  
  Purchase #7 $138.81   9.447%   $151.9234   $151.92   $151.90   $151.90  
  7 purchase totals = $946.17       $1,058.2479   $1,058.25   $1,058.25   $1,058.30