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 $55.68   13.686%   $63.3004   $63.30   $63.30   $63.30  
  Purchase #2 $157.54   6.746%   $168.1676   $168.17   $168.15   $168.20  
  Purchase #3 $97.34   6.371%   $103.5415   $103.54   $103.55   $103.50  
  Purchase #4 $33.82   13.671%   $38.4435   $38.44   $38.45   $38.40  
  Purchase #5 $248.40   4.139%   $258.6813   $258.68   $258.70   $258.70  
  Purchase #6 $203.33   11.338%   $226.3836   $226.38   $226.40   $226.40  
  Purchase #7 $74.90   13.343%   $84.8939   $84.89   $84.90   $84.90  
  7 purchase totals = $871.01       $943.4118   $943.40   $943.45   $943.40