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 $6.82   11.510%   $7.605   $7.61   $7.60   $7.60  
  Purchase #2 $239.76   8.396%   $259.8902   $259.89   $259.90   $259.90  
  Purchase #3 $119.73   11.713%   $133.754   $133.75   $133.75   $133.80  
  Purchase #4 $161.65   7.516%   $173.7996   $173.80   $173.80   $173.80  
  Purchase #5 $125.32   8.537%   $136.0186   $136.02   $136.00   $136.00  
  Purchase #6 $110.26   4.248%   $114.9438   $114.94   $114.95   $114.90  
  Purchase #7 $207.70   7.151%   $222.5526   $222.55   $222.55   $222.60  
  7 purchase totals = $971.24       $1,048.5638   $1,048.56   $1,048.55   $1,048.60