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 $24.93   6.775%   $26.619   $26.62   $26.60   $26.60  
  Purchase #2 $218.68   13.165%   $247.4692   $247.47   $247.45   $247.50  
  Purchase #3 $96.93   10.553%   $107.159   $107.16   $107.15   $107.20  
  Purchase #4 $59.27   8.203%   $64.1319   $64.13   $64.15   $64.10  
  Purchase #5 $144.71   8.497%   $157.006   $157.01   $157.00   $157.00  
  Purchase #6 $235.91   5.515%   $248.9204   $248.92   $248.90   $248.90  
  Purchase #7 $108.68   11.218%   $120.8717   $120.87   $120.85   $120.90  
  7 purchase totals = $889.11       $972.1772   $972.18   $972.10   $972.20