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 $71.95   10.430%   $79.4544   $79.45   $79.45   $79.50  
  Purchase #2 $249.70   6.553%   $266.0628   $266.06   $266.05   $266.10  
  Purchase #3 $139.90   9.193%   $152.761   $152.76   $152.75   $152.80  
  Purchase #4 $175.84   5.604%   $185.6941   $185.69   $185.70   $185.70  
  Purchase #5 $93.88   13.318%   $106.3829   $106.38   $106.40   $106.40  
  Purchase #6 $192.58   9.424%   $210.7287   $210.73   $210.75   $210.70  
  Purchase #7 $31.84   3.481%   $32.9484   $32.95   $32.95   $32.90  
  7 purchase totals = $955.69       $1,034.0323   $1,034.02   $1,034.05   $1,034.10