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 $85.98   12.267%   $96.5272   $96.53   $96.55   $96.50  
  Purchase #2 $87.88   6.542%   $93.6291   $93.63   $93.65   $93.60  
  Purchase #3 $8.28   11.706%   $9.2493   $9.25   $9.25   $9.20  
  Purchase #4 $187.34   7.795%   $201.9432   $201.94   $201.95   $201.90  
  Purchase #5 $96.93   8.806%   $105.4657   $105.47   $105.45   $105.50  
  Purchase #6 $49.79   8.276%   $53.9106   $53.91   $53.90   $53.90  
  Purchase #7 $165.88   7.756%   $178.7457   $178.75   $178.75   $178.70  
  7 purchase totals = $682.08       $739.4708   $739.48   $739.50   $739.30