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 $113.78   10.774%   $126.0387   $126.04   $126.05   $126.00  
  Purchase #2 $35.48   8.864%   $38.6249   $38.62   $38.60   $38.60  
  Purchase #3 $208.32   13.138%   $235.6891   $235.69   $235.70   $235.70  
  Purchase #4 $53.62   11.538%   $59.8067   $59.81   $59.80   $59.80  
  Purchase #5 $78.46   8.465%   $85.1016   $85.10   $85.10   $85.10  
  Purchase #6 $12.93   4.705%   $13.5384   $13.54   $13.55   $13.50  
  Purchase #7 $177.39   13.312%   $201.0042   $201.00   $201.00   $201.00  
  7 purchase totals = $679.98       $759.8036   $759.80   $759.80   $759.70