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 $167.33   11.177%   $186.0325   $186.03   $186.05   $186.00  
  Purchase #2 $34.43   4.286%   $35.9057   $35.91   $35.90   $35.90  
  Purchase #3 $119.25   5.802%   $126.1689   $126.17   $126.15   $126.20  
  Purchase #4 $58.99   6.711%   $62.9488   $62.95   $62.95   $62.90  
  Purchase #5 $241.40   3.356%   $249.5014   $249.50   $249.50   $249.50  
  Purchase #6 $44.81   10.218%   $49.3887   $49.39   $49.40   $49.40  
  Purchase #7 $149.61   12.701%   $168.612   $168.61   $168.60   $168.60  
  7 purchase totals = $815.82       $878.5580   $878.56   $878.55   $878.50