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 $61.81   5.572%   $65.2541   $65.25   $65.25   $65.30  
  Purchase #2 $211.64   4.857%   $221.9194   $221.92   $221.90   $221.90  
  Purchase #3 $118.30   13.718%   $134.5284   $134.53   $134.55   $134.50  
  Purchase #4 $100.28   5.200%   $105.4946   $105.49   $105.50   $105.50  
  Purchase #5 $74.59   9.206%   $81.4568   $81.46   $81.45   $81.50  
  Purchase #6 $69.55   6.651%   $74.1758   $74.18   $74.20   $74.20  
  Purchase #7 $119.38   13.608%   $135.6252   $135.63   $135.65   $135.60  
  7 purchase totals = $755.55       $818.4543   $818.46   $818.50   $818.50