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 $250.31   4.830%   $262.4   $262.40   $262.40   $262.40  
  Purchase #2 $211.38   3.805%   $219.423   $219.42   $219.40   $219.40  
  Purchase #3 $201.54   10.116%   $221.9278   $221.93   $221.95   $221.90  
  Purchase #4 $38.71   12.324%   $43.4806   $43.48   $43.50   $43.50  
  Purchase #5 $202.74   5.504%   $213.8988   $213.90   $213.90   $213.90  
  Purchase #6 $166.77   8.381%   $180.747   $180.75   $180.75   $180.70  
  Purchase #7 $95.55   6.165%   $101.4407   $101.44   $101.45   $101.40  
  7 purchase totals = $1,167.00       $1,243.3179   $1,243.32   $1,243.35   $1,243.20