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 $175.44   11.768%   $196.0858   $196.09   $196.10   $196.10  
  Purchase #2 $221.31   7.342%   $237.5586   $237.56   $237.55   $237.60  
  Purchase #3 $75.84   13.691%   $86.2233   $86.22   $86.20   $86.20  
  Purchase #4 $248.97   7.262%   $267.0502   $267.05   $267.05   $267.10  
  Purchase #5 $154.75   4.308%   $161.4166   $161.42   $161.40   $161.40  
  Purchase #6 $201.56   8.461%   $218.614   $218.61   $218.60   $218.60  
  Purchase #7 $250.77   13.330%   $284.1976   $284.20   $284.20   $284.20  
  7 purchase totals = $1,328.64       $1,451.1461   $1,451.15   $1,451.10   $1,451.20