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 $127.95   5.409%   $134.8708   $134.87   $134.85   $134.90  
  Purchase #2 $113.51   7.735%   $122.29   $122.29   $122.30   $122.30  
  Purchase #3 $24.99   11.608%   $27.8908   $27.89   $27.90   $27.90  
  Purchase #4 $164.37   10.569%   $181.7423   $181.74   $181.75   $181.70  
  Purchase #5 $189.31   10.218%   $208.6537   $208.65   $208.65   $208.70  
  Purchase #6 $171.37   7.688%   $184.5449   $184.54   $184.55   $184.50  
  Purchase #7 $72.40   5.663%   $76.5   $76.50   $76.50   $76.50  
  7 purchase totals = $863.90       $936.4925   $936.48   $936.50   $936.50