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 $82.72   6.391%   $88.0066   $88.01   $88.00   $88.00  
  Purchase #2 $111.74   5.617%   $118.0164   $118.02   $118.00   $118.00  
  Purchase #3 $188.35   13.117%   $213.0559   $213.06   $213.05   $213.10  
  Purchase #4 $183.76   9.721%   $201.6233   $201.62   $201.60   $201.60  
  Purchase #5 $76.66   9.584%   $84.0071   $84.01   $84.00   $84.00  
  Purchase #6 $59.58   11.634%   $66.5115   $66.51   $66.50   $66.50  
  Purchase #7 $72.41   8.280%   $78.4055   $78.41   $78.40   $78.40  
  7 purchase totals = $775.22       $849.6263   $849.64   $849.55   $849.60