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 $111.88   12.859%   $126.2666   $126.27   $126.25   $126.30  
  Purchase #2 $94.40   10.758%   $104.5556   $104.56   $104.55   $104.60  
  Purchase #3 $37.79   8.501%   $41.0025   $41.00   $41.00   $41.00  
  Purchase #4 $62.31   6.769%   $66.5278   $66.53   $66.55   $66.50  
  Purchase #5 $146.78   4.102%   $152.8009   $152.80   $152.80   $152.80  
  Purchase #6 $215.89   8.451%   $234.1349   $234.13   $234.15   $234.10  
  Purchase #7 $9.87   8.717%   $10.7304   $10.73   $10.75   $10.70  
  7 purchase totals = $678.92       $736.0187   $736.02   $736.05   $736.00