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 $58.69   4.457%   $61.3058   $61.31   $61.30   $61.30  
  Purchase #2 $239.99   3.144%   $247.5353   $247.54   $247.55   $247.50  
  Purchase #3 $24.94   9.281%   $27.2547   $27.25   $27.25   $27.30  
  Purchase #4 $191.78   11.845%   $214.4963   $214.50   $214.50   $214.50  
  Purchase #5 $240.76   7.466%   $258.7351   $258.74   $258.75   $258.70  
  Purchase #6 $34.89   4.455%   $36.4443   $36.44   $36.45   $36.40  
  Purchase #7 $8.41   5.665%   $8.8864   $8.89   $8.90   $8.90  
  7 purchase totals = $799.46       $854.6579   $854.67   $854.70   $854.60