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 $169.83   3.802%   $176.2869   $176.29   $176.30   $176.30  
  Purchase #2 $239.58   4.712%   $250.869   $250.87   $250.85   $250.90  
  Purchase #3 $78.28   13.141%   $88.5668   $88.57   $88.55   $88.60  
  Purchase #4 $169.81   4.655%   $177.7147   $177.71   $177.70   $177.70  
  Purchase #5 $68.87   11.338%   $76.6785   $76.68   $76.70   $76.70  
  Purchase #6 $164.93   4.523%   $172.3898   $172.39   $172.40   $172.40  
  Purchase #7 $9.42   7.697%   $10.1451   $10.15   $10.15   $10.10  
  7 purchase totals = $900.72       $952.6508   $952.66   $952.65   $952.70