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 $33.38   4.329%   $34.825   $34.83   $34.85   $34.80  
  Purchase #2 $185.87   8.114%   $200.9515   $200.95   $200.95   $201.00  
  Purchase #3 $169.37   12.477%   $190.5023   $190.50   $190.50   $190.50  
  Purchase #4 $154.41   10.114%   $170.027   $170.03   $170.05   $170.00  
  Purchase #5 $72.42   12.792%   $81.684   $81.68   $81.70   $81.70  
  Purchase #6 $160.58   13.368%   $182.0463   $182.05   $182.05   $182.00  
  Purchase #7 $161.46   8.173%   $174.6561   $174.66   $174.65   $174.70  
  7 purchase totals = $937.49       $1,034.6922   $1,034.70   $1,034.75   $1,034.70