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 $245.74   7.537%   $264.2614   $264.26   $264.25   $264.30  
  Purchase #2 $207.77   13.116%   $235.0211   $235.02   $235.00   $235.00  
  Purchase #3 $16.71   8.516%   $18.133   $18.13   $18.15   $18.10  
  Purchase #4 $157.48   4.485%   $164.543   $164.54   $164.55   $164.50  
  Purchase #5 $47.38   4.409%   $49.469   $49.47   $49.45   $49.50  
  Purchase #6 $23.93   9.199%   $26.1313   $26.13   $26.15   $26.10  
  Purchase #7 $196.88   3.816%   $204.3929   $204.39   $204.40   $204.40  
  7 purchase totals = $895.89       $961.9517   $961.94   $961.95   $961.90