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 $208.70   13.873%   $237.653   $237.65   $237.65   $237.70  
  Purchase #2 $32.31   5.122%   $33.9649   $33.96   $33.95   $34.00  
  Purchase #3 $181.28   13.671%   $206.0628   $206.06   $206.05   $206.10  
  Purchase #4 $151.78   4.499%   $158.6086   $158.61   $158.60   $158.60  
  Purchase #5 $46.58   11.825%   $52.0881   $52.09   $52.10   $52.10  
  Purchase #6 $80.75   11.752%   $90.2397   $90.24   $90.25   $90.20  
  Purchase #7 $77.33   5.387%   $81.4958   $81.50   $81.50   $81.50  
  7 purchase totals = $778.73       $860.1129   $860.11   $860.10   $860.20