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 $218.66   13.516%   $248.2141   $248.21   $248.20   $248.20  
  Purchase #2 $220.69   5.340%   $232.4748   $232.47   $232.45   $232.50  
  Purchase #3 $233.71   10.473%   $258.1864   $258.19   $258.20   $258.20  
  Purchase #4 $26.78   3.260%   $27.653   $27.65   $27.65   $27.70  
  Purchase #5 $49.57   12.523%   $55.7777   $55.78   $55.80   $55.80  
  Purchase #6 $126.92   3.812%   $131.7582   $131.76   $131.75   $131.80  
  Purchase #7 $7.37   11.349%   $8.2064   $8.21   $8.20   $8.20  
  7 purchase totals = $883.70       $962.2706   $962.27   $962.25   $962.40