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 $202.66   8.533%   $219.953   $219.95   $219.95   $220.00  
  Purchase #2 $12.94   12.522%   $14.5603   $14.56   $14.55   $14.60  
  Purchase #3 $68.64   10.463%   $75.8218   $75.82   $75.80   $75.80  
  Purchase #4 $104.45   7.699%   $112.4916   $112.49   $112.50   $112.50  
  Purchase #5 $71.74   13.116%   $81.1494   $81.15   $81.15   $81.10  
  Purchase #6 $122.78   9.582%   $134.5448   $134.54   $134.55   $134.50  
  Purchase #7 $34.26   10.833%   $37.9714   $37.97   $37.95   $38.00  
  7 purchase totals = $617.47       $676.4923   $676.48   $676.45   $676.50