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 $49.71   13.266%   $56.3045   $56.30   $56.30   $56.30  
  Purchase #2 $240.40   9.680%   $263.6707   $263.67   $263.65   $263.70  
  Purchase #3 $234.59   13.715%   $266.764   $266.76   $266.75   $266.80  
  Purchase #4 $182.98   9.264%   $199.9313   $199.93   $199.95   $199.90  
  Purchase #5 $136.47   7.872%   $147.2129   $147.21   $147.20   $147.20  
  Purchase #6 $108.91   3.174%   $112.3668   $112.37   $112.35   $112.40  
  Purchase #7 $20.35   5.715%   $21.513   $21.51   $21.50   $21.50  
  7 purchase totals = $973.41       $1,067.7632   $1,067.75   $1,067.70   $1,067.80