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 $55.95   9.239%   $61.1192   $61.12   $61.10   $61.10  
  Purchase #2 $163.79   8.347%   $177.4616   $177.46   $177.45   $177.50  
  Purchase #3 $158.66   3.817%   $164.7161   $164.72   $164.70   $164.70  
  Purchase #4 $56.84   3.317%   $58.7254   $58.73   $58.75   $58.70  
  Purchase #5 $134.42   3.449%   $139.0561   $139.06   $139.05   $139.10  
  Purchase #6 $102.26   6.811%   $109.2249   $109.22   $109.20   $109.20  
  Purchase #7 $241.94   10.307%   $266.8768   $266.88   $266.90   $266.90  
  7 purchase totals = $913.86       $977.1801   $977.19   $977.15   $977.20