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 $87.38   5.308%   $92.0181   $92.02   $92.00   $92.00  
  Purchase #2 $83.93   13.847%   $95.5518   $95.55   $95.55   $95.60  
  Purchase #3 $113.26   8.326%   $122.69   $122.69   $122.70   $122.70  
  Purchase #4 $198.36   5.864%   $209.9918   $209.99   $210.00   $210.00  
  Purchase #5 $120.29   3.275%   $124.2295   $124.23   $124.25   $124.20  
  Purchase #6 $36.55   9.515%   $40.0277   $40.03   $40.05   $40.00  
  Purchase #7 $223.25   12.209%   $250.5066   $250.51   $250.50   $250.50  
  7 purchase totals = $863.02       $935.0155   $935.02   $935.05   $935.00