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 $58.45   5.822%   $61.853   $61.85   $61.85   $61.90  
  Purchase #2 $72.42   6.331%   $77.0049   $77.00   $77.00   $77.00  
  Purchase #3 $201.95   5.776%   $213.6146   $213.61   $213.60   $213.60  
  Purchase #4 $228.77   11.362%   $254.7628   $254.76   $254.75   $254.80  
  Purchase #5 $170.44   7.594%   $183.3832   $183.38   $183.40   $183.40  
  Purchase #6 $23.60   13.860%   $26.871   $26.87   $26.85   $26.90  
  Purchase #7 $38.76   8.427%   $42.0263   $42.03   $42.05   $42.00  
  7 purchase totals = $794.39       $859.5158   $859.50   $859.50   $859.60