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 $93.84   3.858%   $97.4603   $97.46   $97.45   $97.50  
  Purchase #2 $234.99   12.626%   $264.6598   $264.66   $264.65   $264.70  
  Purchase #3 $160.51   8.799%   $174.6333   $174.63   $174.65   $174.60  
  Purchase #4 $107.38   11.615%   $119.8522   $119.85   $119.85   $119.90  
  Purchase #5 $71.30   10.154%   $78.5398   $78.54   $78.55   $78.50  
  Purchase #6 $34.59   3.315%   $35.7367   $35.74   $35.75   $35.70  
  Purchase #7 $97.84   6.655%   $104.3513   $104.35   $104.35   $104.40  
  7 purchase totals = $800.45       $875.2334   $875.23   $875.25   $875.30