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 $46.96   5.493%   $49.5395   $49.54   $49.55   $49.50  
  Purchase #2 $16.80   8.393%   $18.21   $18.21   $18.20   $18.20  
  Purchase #3 $173.55   7.481%   $186.5333   $186.53   $186.55   $186.50  
  Purchase #4 $157.25   5.758%   $166.3045   $166.30   $166.30   $166.30  
  Purchase #5 $248.89   9.658%   $272.9278   $272.93   $272.95   $272.90  
  Purchase #6 $37.43   11.865%   $41.8711   $41.87   $41.85   $41.90  
  Purchase #7 $151.33   13.560%   $171.8503   $171.85   $171.85   $171.90  
  7 purchase totals = $832.21       $907.2365   $907.23   $907.25   $907.20