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 $71.41   3.177%   $73.6787   $73.68   $73.70   $73.70  
  Purchase #2 $41.79   13.839%   $47.5733   $47.57   $47.55   $47.60  
  Purchase #3 $16.48   9.182%   $17.9932   $17.99   $18.00   $18.00  
  Purchase #4 $39.49   3.148%   $40.7331   $40.73   $40.75   $40.70  
  Purchase #5 $179.45   4.534%   $187.5863   $187.59   $187.60   $187.60  
  Purchase #6 $178.52   5.309%   $187.9976   $188.00   $188.00   $188.00  
  Purchase #7 $228.87   10.522%   $252.9517   $252.95   $252.95   $253.00  
  7 purchase totals = $756.01       $808.5139   $808.51   $808.55   $808.60