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 $68.83   7.812%   $74.207   $74.21   $74.20   $74.20  
  Purchase #2 $239.50   9.266%   $261.6921   $261.69   $261.70   $261.70  
  Purchase #3 $54.77   5.325%   $57.6865   $57.69   $57.70   $57.70  
  Purchase #4 $189.44   6.190%   $201.1663   $201.17   $201.15   $201.20  
  Purchase #5 $162.54   7.269%   $174.355   $174.36   $174.35   $174.40  
  Purchase #6 $34.84   8.833%   $37.9174   $37.92   $37.90   $37.90  
  Purchase #7 $75.74   3.688%   $78.5333   $78.53   $78.55   $78.50  
  7 purchase totals = $825.66       $885.5576   $885.57   $885.55   $885.60