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 $107.25   11.106%   $119.1612   $119.16   $119.15   $119.20  
  Purchase #2 $141.32   7.675%   $152.1663   $152.17   $152.15   $152.20  
  Purchase #3 $115.45   12.423%   $129.7924   $129.79   $129.80   $129.80  
  Purchase #4 $231.91   8.758%   $252.2207   $252.22   $252.20   $252.20  
  Purchase #5 $38.29   9.421%   $41.8973   $41.90   $41.90   $41.90  
  Purchase #6 $85.40   12.379%   $95.9717   $95.97   $95.95   $96.00  
  Purchase #7 $210.34   12.575%   $236.7903   $236.79   $236.80   $236.80  
  7 purchase totals = $929.96       $1,027.9999   $1,028.00   $1,027.95   $1,028.10