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 $182.80   3.520%   $189.2346   $189.23   $189.25   $189.20  
  Purchase #2 $53.54   3.251%   $55.2806   $55.28   $55.30   $55.30  
  Purchase #3 $239.46   8.418%   $259.6177   $259.62   $259.60   $259.60  
  Purchase #4 $246.81   11.722%   $275.7411   $275.74   $275.75   $275.70  
  Purchase #5 $162.88   3.775%   $169.0287   $169.03   $169.05   $169.00  
  Purchase #6 $95.46   3.289%   $98.5997   $98.60   $98.60   $98.60  
  Purchase #7 $201.97   7.136%   $216.3826   $216.38   $216.40   $216.40  
  7 purchase totals = $1,182.92       $1,263.8850   $1,263.88   $1,263.95   $1,263.80