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 $191.35   6.689%   $204.1494   $204.15   $204.15   $204.10  
  Purchase #2 $119.87   5.807%   $126.8309   $126.83   $126.85   $126.80  
  Purchase #3 $35.80   8.676%   $38.906   $38.91   $38.90   $38.90  
  Purchase #4 $64.52   11.398%   $71.874   $71.87   $71.85   $71.90  
  Purchase #5 $239.81   4.317%   $250.1626   $250.16   $250.15   $250.20  
  Purchase #6 $88.46   3.420%   $91.4853   $91.49   $91.50   $91.50  
  Purchase #7 $89.28   4.241%   $93.0664   $93.07   $93.05   $93.10  
  7 purchase totals = $829.09       $876.4746   $876.48   $876.45   $876.50