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 $42.99   13.240%   $48.6819   $48.68   $48.70   $48.70  
  Purchase #2 $190.83   8.337%   $206.7395   $206.74   $206.75   $206.70  
  Purchase #3 $157.30   5.591%   $166.0946   $166.09   $166.10   $166.10  
  Purchase #4 $205.85   3.188%   $212.4125   $212.41   $212.40   $212.40  
  Purchase #5 $30.57   11.234%   $34.0042   $34.00   $34.00   $34.00  
  Purchase #6 $185.35   12.603%   $208.7097   $208.71   $208.70   $208.70  
  Purchase #7 $111.64   5.862%   $118.1843   $118.18   $118.20   $118.20  
  7 purchase totals = $924.53       $994.8267   $994.81   $994.85   $994.80