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 $24.64   5.646%   $26.0312   $26.03   $26.05   $26.00  
  Purchase #2 $39.46   12.353%   $44.3345   $44.33   $44.35   $44.30  
  Purchase #3 $174.89   13.640%   $198.745   $198.75   $198.75   $198.70  
  Purchase #4 $153.87   13.697%   $174.9456   $174.95   $174.95   $174.90  
  Purchase #5 $99.50   3.689%   $103.1706   $103.17   $103.15   $103.20  
  Purchase #6 $56.89   4.330%   $59.3533   $59.35   $59.35   $59.40  
  Purchase #7 $66.62   13.224%   $75.4298   $75.43   $75.45   $75.40  
  7 purchase totals = $615.87       $682.0100   $682.01   $682.05   $681.90