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 $134.73   4.873%   $141.2954   $141.30   $141.30   $141.30  
  Purchase #2 $166.58   9.292%   $182.0586   $182.06   $182.05   $182.10  
  Purchase #3 $42.77   8.805%   $46.5359   $46.54   $46.55   $46.50  
  Purchase #4 $186.65   8.149%   $201.8601   $201.86   $201.85   $201.90  
  Purchase #5 $5.91   13.518%   $6.7089   $6.71   $6.70   $6.70  
  Purchase #6 $113.45   8.622%   $123.2317   $123.23   $123.25   $123.20  
  Purchase #7 $182.47   8.286%   $197.5895   $197.59   $197.60   $197.60  
  7 purchase totals = $832.56       $899.2801   $899.29   $899.30   $899.30