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 $126.38   6.476%   $134.5644   $134.56   $134.55   $134.60  
  Purchase #2 $220.65   13.611%   $250.6827   $250.68   $250.70   $250.70  
  Purchase #3 $239.27   8.578%   $259.7946   $259.79   $259.80   $259.80  
  Purchase #4 $225.42   13.340%   $255.491   $255.49   $255.50   $255.50  
  Purchase #5 $9.32   8.761%   $10.1365   $10.14   $10.15   $10.10  
  Purchase #6 $124.25   7.624%   $133.7228   $133.72   $133.70   $133.70  
  Purchase #7 $163.57   7.697%   $176.16   $176.16   $176.15   $176.20  
  7 purchase totals = $1,108.86       $1,220.5520   $1,220.54   $1,220.55   $1,220.60