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 $247.93   11.835%   $277.2725   $277.27   $277.25   $277.30  
  Purchase #2 $159.34   5.292%   $167.7723   $167.77   $167.75   $167.80  
  Purchase #3 $9.53   9.706%   $10.455   $10.46   $10.45   $10.50  
  Purchase #4 $95.30   3.170%   $98.321   $98.32   $98.30   $98.30  
  Purchase #5 $20.82   12.464%   $23.415   $23.42   $23.40   $23.40  
  Purchase #6 $223.76   5.542%   $236.1608   $236.16   $236.15   $236.20  
  Purchase #7 $42.61   11.380%   $47.459   $47.46   $47.45   $47.50  
  7 purchase totals = $799.29       $860.8556   $860.86   $860.75   $861.00