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 $161.67   8.405%   $175.2584   $175.26   $175.25   $175.30  
  Purchase #2 $22.74   7.491%   $24.4435   $24.44   $24.45   $24.40  
  Purchase #3 $48.65   10.409%   $53.714   $53.71   $53.70   $53.70  
  Purchase #4 $20.64   10.225%   $22.7504   $22.75   $22.75   $22.80  
  Purchase #5 $175.89   13.666%   $199.9271   $199.93   $199.95   $199.90  
  Purchase #6 $141.31   7.864%   $152.4226   $152.42   $152.40   $152.40  
  Purchase #7 $71.81   6.825%   $76.711   $76.71   $76.70   $76.70  
  7 purchase totals = $642.71       $705.2270   $705.22   $705.20   $705.20