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 $124.72   11.652%   $139.2524   $139.25   $139.25   $139.30  
  Purchase #2 $250.94   9.285%   $274.2398   $274.24   $274.25   $274.20  
  Purchase #3 $50.45   12.387%   $56.6992   $56.70   $56.70   $56.70  
  Purchase #4 $23.27   7.298%   $24.9682   $24.97   $24.95   $25.00  
  Purchase #5 $180.95   8.409%   $196.1661   $196.17   $196.15   $196.20  
  Purchase #6 $183.73   5.323%   $193.5099   $193.51   $193.50   $193.50  
  Purchase #7 $155.44   12.664%   $175.1249   $175.12   $175.10   $175.10  
  7 purchase totals = $969.50       $1,059.9605   $1,059.96   $1,059.90   $1,060.00