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 $231.34   11.386%   $257.6804   $257.68   $257.70   $257.70  
  Purchase #2 $26.66   12.858%   $30.0879   $30.09   $30.10   $30.10  
  Purchase #3 $126.26   7.264%   $135.4315   $135.43   $135.45   $135.40  
  Purchase #4 $31.95   4.858%   $33.5021   $33.50   $33.50   $33.50  
  Purchase #5 $216.79   12.412%   $243.698   $243.70   $243.70   $243.70  
  Purchase #6 $124.68   13.843%   $141.9395   $141.94   $141.95   $141.90  
  Purchase #7 $182.25   13.186%   $206.2815   $206.28   $206.30   $206.30  
  7 purchase totals = $939.93       $1,048.6209   $1,048.62   $1,048.70   $1,048.60