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 $24.67   3.283%   $25.4799   $25.48   $25.50   $25.50  
  Purchase #2 $96.93   6.270%   $103.0075   $103.01   $103.00   $103.00  
  Purchase #3 $213.70   6.587%   $227.7764   $227.78   $227.80   $227.80  
  Purchase #4 $191.78   10.397%   $211.7194   $211.72   $211.70   $211.70  
  Purchase #5 $214.92   11.227%   $239.0491   $239.05   $239.05   $239.00  
  Purchase #6 $212.28   13.103%   $240.095   $240.10   $240.10   $240.10  
  Purchase #7 $183.38   5.655%   $193.7501   $193.75   $193.75   $193.80  
  7 purchase totals = $1,137.66       $1,240.8774   $1,240.89   $1,240.90   $1,240.90