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 $94.61   13.773%   $107.6406   $107.64   $107.65   $107.60  
  Purchase #2 $218.46   12.354%   $245.4485   $245.45   $245.45   $245.40  
  Purchase #3 $189.35   10.188%   $208.641   $208.64   $208.65   $208.60  
  Purchase #4 $41.39   11.475%   $46.1395   $46.14   $46.15   $46.10  
  Purchase #5 $194.67   10.787%   $215.6691   $215.67   $215.65   $215.70  
  Purchase #6 $18.99   10.544%   $20.9923   $20.99   $21.00   $21.00  
  Purchase #7 $96.46   13.176%   $109.1696   $109.17   $109.15   $109.20  
  7 purchase totals = $853.93       $953.7006   $953.70   $953.70   $953.60