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 $86.82   13.651%   $98.6718   $98.67   $98.65   $98.70  
  Purchase #2 $111.68   12.515%   $125.6568   $125.66   $125.65   $125.70  
  Purchase #3 $194.54   3.425%   $201.203   $201.20   $201.20   $201.20  
  Purchase #4 $227.92   9.577%   $249.7479   $249.75   $249.75   $249.70  
  Purchase #5 $35.99   8.605%   $39.0869   $39.09   $39.10   $39.10  
  Purchase #6 $30.92   11.683%   $34.5324   $34.53   $34.55   $34.50  
  Purchase #7 $174.51   8.158%   $188.7465   $188.75   $188.75   $188.70  
  7 purchase totals = $862.38       $937.6453   $937.65   $937.65   $937.60