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 $168.27   5.347%   $177.2674   $177.27   $177.25   $177.30  
  Purchase #2 $126.35   8.131%   $136.6235   $136.62   $136.60   $136.60  
  Purchase #3 $19.43   11.106%   $21.5879   $21.59   $21.60   $21.60  
  Purchase #4 $30.54   13.561%   $34.6815   $34.68   $34.70   $34.70  
  Purchase #5 $162.30   8.561%   $176.1945   $176.19   $176.20   $176.20  
  Purchase #6 $224.40   10.742%   $248.505   $248.51   $248.50   $248.50  
  Purchase #7 $58.99   12.448%   $66.3331   $66.33   $66.35   $66.30  
  7 purchase totals = $790.28       $861.1929   $861.19   $861.20   $861.20