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 $86.37   13.418%   $97.9591   $97.96   $97.95   $98.00  
  Purchase #2 $235.66   13.148%   $266.6446   $266.64   $266.65   $266.60  
  Purchase #3 $82.67   4.213%   $86.1529   $86.15   $86.15   $86.20  
  Purchase #4 $246.63   8.271%   $267.0288   $267.03   $267.05   $267.00  
  Purchase #5 $149.31   3.321%   $154.2686   $154.27   $154.25   $154.30  
  Purchase #6 $49.37   4.408%   $51.5462   $51.55   $51.55   $51.50  
  Purchase #7 $10.33   10.641%   $11.4292   $11.43   $11.45   $11.40  
  7 purchase totals = $860.34       $935.0294   $935.03   $935.05   $935.00