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 $49.77   12.588%   $56.035   $56.04   $56.05   $56.00  
  Purchase #2 $199.32   13.745%   $226.7165   $226.72   $226.70   $226.70  
  Purchase #3 $54.47   4.606%   $56.9789   $56.98   $57.00   $57.00  
  Purchase #4 $180.81   3.461%   $187.0678   $187.07   $187.05   $187.10  
  Purchase #5 $70.99   4.626%   $74.274   $74.27   $74.25   $74.30  
  Purchase #6 $193.54   8.473%   $209.9386   $209.94   $209.95   $209.90  
  Purchase #7 $138.64   13.155%   $156.8781   $156.88   $156.90   $156.90  
  7 purchase totals = $887.54       $967.8889   $967.90   $967.90   $967.90