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 $76.60   9.257%   $83.6909   $83.69   $83.70   $83.70  
  Purchase #2 $24.77   4.856%   $25.9728   $25.97   $25.95   $26.00  
  Purchase #3 $45.83   11.138%   $50.9345   $50.93   $50.95   $50.90  
  Purchase #4 $59.41   3.863%   $61.705   $61.71   $61.70   $61.70  
  Purchase #5 $23.90   11.805%   $26.7214   $26.72   $26.70   $26.70  
  Purchase #6 $44.47   4.766%   $46.5894   $46.59   $46.60   $46.60  
  Purchase #7 $216.42   3.776%   $224.592   $224.59   $224.60   $224.60  
  7 purchase totals = $491.40       $520.2060   $520.20   $520.20   $520.20