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 $81.75   4.463%   $85.3985   $85.40   $85.40   $85.40  
  Purchase #2 $84.51   13.866%   $96.2282   $96.23   $96.25   $96.20  
  Purchase #3 $110.94   6.295%   $117.9237   $117.92   $117.90   $117.90  
  Purchase #4 $81.38   12.707%   $91.721   $91.72   $91.70   $91.70  
  Purchase #5 $46.56   10.705%   $51.5442   $51.54   $51.55   $51.50  
  Purchase #6 $66.74   13.225%   $75.5664   $75.57   $75.55   $75.60  
  Purchase #7 $225.63   4.455%   $235.6818   $235.68   $235.70   $235.70  
  7 purchase totals = $697.51       $754.0638   $754.06   $754.05   $754.00