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 $208.38   13.546%   $236.6072   $236.61   $236.60   $236.60  
  Purchase #2 $175.33   9.217%   $191.4902   $191.49   $191.50   $191.50  
  Purchase #3 $225.67   11.205%   $250.9563   $250.96   $250.95   $251.00  
  Purchase #4 $236.31   11.471%   $263.4171   $263.42   $263.40   $263.40  
  Purchase #5 $11.69   4.492%   $12.2151   $12.22   $12.20   $12.20  
  Purchase #6 $193.34   11.855%   $216.2605   $216.26   $216.25   $216.30  
  Purchase #7 $206.91   8.112%   $223.6945   $223.69   $223.70   $223.70  
  7 purchase totals = $1,257.63       $1,394.6409   $1,394.65   $1,394.60   $1,394.70