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 $49.75   13.184%   $56.309   $56.31   $56.30   $56.30  
  Purchase #2 $90.66   8.867%   $98.6988   $98.70   $98.70   $98.70  
  Purchase #3 $160.85   3.765%   $166.906   $166.91   $166.90   $166.90  
  Purchase #4 $36.41   11.712%   $40.6743   $40.67   $40.65   $40.70  
  Purchase #5 $65.76   10.533%   $72.6865   $72.69   $72.70   $72.70  
  Purchase #6 $201.44   11.697%   $225.0024   $225.00   $225.00   $225.00  
  Purchase #7 $71.35   5.461%   $75.2464   $75.25   $75.25   $75.20  
  7 purchase totals = $676.22       $735.5234   $735.53   $735.50   $735.50