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 $88.63   8.642%   $96.2894   $96.29   $96.30   $96.30  
  Purchase #2 $136.81   6.763%   $146.0625   $146.06   $146.05   $146.10  
  Purchase #3 $29.68   5.572%   $31.3338   $31.33   $31.35   $31.30  
  Purchase #4 $235.28   8.500%   $255.2788   $255.28   $255.30   $255.30  
  Purchase #5 $51.72   12.271%   $58.0666   $58.07   $58.05   $58.10  
  Purchase #6 $224.93   5.672%   $237.688   $237.69   $237.70   $237.70  
  Purchase #7 $55.64   7.662%   $59.9031   $59.90   $59.90   $59.90  
  7 purchase totals = $822.69       $884.6222   $884.62   $884.65   $884.70