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 $239.91   10.450%   $264.9806   $264.98   $265.00   $265.00  
  Purchase #2 $111.38   6.808%   $118.9628   $118.96   $118.95   $119.00  
  Purchase #3 $43.63   6.306%   $46.3813   $46.38   $46.40   $46.40  
  Purchase #4 $182.49   6.743%   $194.7953   $194.80   $194.80   $194.80  
  Purchase #5 $113.28   8.280%   $122.6596   $122.66   $122.65   $122.70  
  Purchase #6 $53.73   5.866%   $56.8818   $56.88   $56.90   $56.90  
  Purchase #7 $208.33   3.685%   $216.007   $216.01   $216.00   $216.00  
  7 purchase totals = $952.75       $1,020.6684   $1,020.67   $1,020.70   $1,020.80