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 $163.34   8.105%   $176.5787   $176.58   $176.60   $176.60  
  Purchase #2 $247.42   11.565%   $276.0341   $276.03   $276.05   $276.00  
  Purchase #3 $24.33   11.515%   $27.1316   $27.13   $27.15   $27.10  
  Purchase #4 $215.38   9.573%   $235.9983   $236.00   $236.00   $236.00  
  Purchase #5 $215.25   12.748%   $242.6901   $242.69   $242.70   $242.70  
  Purchase #6 $248.42   5.509%   $262.1055   $262.11   $262.10   $262.10  
  Purchase #7 $15.75   5.341%   $16.5912   $16.59   $16.60   $16.60  
  7 purchase totals = $1,129.89       $1,237.1295   $1,237.13   $1,237.20   $1,237.10