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 $111.49   13.423%   $126.4553   $126.46   $126.45   $126.50  
  Purchase #2 $171.56   12.153%   $192.4097   $192.41   $192.40   $192.40  
  Purchase #3 $102.91   7.677%   $110.8104   $110.81   $110.80   $110.80  
  Purchase #4 $246.70   4.180%   $257.0121   $257.01   $257.00   $257.00  
  Purchase #5 $146.65   10.709%   $162.3547   $162.35   $162.35   $162.40  
  Purchase #6 $51.61   3.866%   $53.6052   $53.61   $53.60   $53.60  
  Purchase #7 $198.57   8.410%   $215.2697   $215.27   $215.25   $215.30  
  7 purchase totals = $1,029.49       $1,117.9171   $1,117.92   $1,117.85   $1,118.00