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 $21.66   13.318%   $24.5447   $24.54   $24.55   $24.50  
  Purchase #2 $69.91   3.500%   $72.3569   $72.36   $72.35   $72.40  
  Purchase #3 $58.77   13.505%   $66.7069   $66.71   $66.70   $66.70  
  Purchase #4 $72.78   3.871%   $75.5973   $75.60   $75.60   $75.60  
  Purchase #5 $104.97   8.745%   $114.1496   $114.15   $114.15   $114.10  
  Purchase #6 $200.99   7.331%   $215.7246   $215.72   $215.70   $215.70  
  Purchase #7 $160.43   5.120%   $168.644   $168.64   $168.65   $168.60  
  7 purchase totals = $689.51       $737.7240   $737.72   $737.70   $737.60