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 $159.48   13.176%   $180.4931   $180.49   $180.50   $180.50  
  Purchase #2 $187.60   8.367%   $203.2965   $203.30   $203.30   $203.30  
  Purchase #3 $88.27   4.447%   $92.1954   $92.20   $92.20   $92.20  
  Purchase #4 $95.93   12.149%   $107.5845   $107.58   $107.60   $107.60  
  Purchase #5 $234.41   13.775%   $266.7   $266.70   $266.70   $266.70  
  Purchase #6 $26.81   5.317%   $28.2355   $28.24   $28.25   $28.20  
  Purchase #7 $44.69   3.344%   $46.1844   $46.18   $46.20   $46.20  
  7 purchase totals = $837.19       $924.6894   $924.69   $924.75   $924.70