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 $201.34   11.659%   $224.8142   $224.81   $224.80   $224.80  
  Purchase #2 $98.60   10.179%   $108.6365   $108.64   $108.65   $108.60  
  Purchase #3 $241.80   12.524%   $272.083   $272.08   $272.10   $272.10  
  Purchase #4 $146.31   12.348%   $164.3764   $164.38   $164.40   $164.40  
  Purchase #5 $240.61   5.520%   $253.8917   $253.89   $253.90   $253.90  
  Purchase #6 $52.68   11.337%   $58.6523   $58.65   $58.65   $58.70  
  Purchase #7 $8.56   7.258%   $9.1813   $9.18   $9.20   $9.20  
  7 purchase totals = $989.90       $1,091.6354   $1,091.63   $1,091.70   $1,091.70