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 $136.34   6.762%   $145.5593   $145.56   $145.55   $145.60  
  Purchase #2 $50.81   11.107%   $56.4535   $56.45   $56.45   $56.50  
  Purchase #3 $228.31   7.838%   $246.2049   $246.20   $246.20   $246.20  
  Purchase #4 $42.40   7.622%   $45.6317   $45.63   $45.65   $45.60  
  Purchase #5 $120.76   9.178%   $131.8434   $131.84   $131.85   $131.80  
  Purchase #6 $249.28   4.689%   $260.9687   $260.97   $260.95   $261.00  
  Purchase #7 $127.44   9.669%   $139.7622   $139.76   $139.75   $139.80  
  7 purchase totals = $955.34       $1,026.4237   $1,026.41   $1,026.40   $1,026.50