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 $105.77   13.311%   $119.849   $119.85   $119.85   $119.80  
  Purchase #2 $38.54   7.744%   $41.5245   $41.52   $41.50   $41.50  
  Purchase #3 $241.53   4.588%   $252.6114   $252.61   $252.60   $252.60  
  Purchase #4 $223.55   5.632%   $236.1403   $236.14   $236.15   $236.10  
  Purchase #5 $27.75   10.125%   $30.5597   $30.56   $30.55   $30.60  
  Purchase #6 $143.96   13.319%   $163.134   $163.13   $163.15   $163.10  
  Purchase #7 $129.33   3.799%   $134.2432   $134.24   $134.25   $134.20  
  7 purchase totals = $910.43       $978.0621   $978.05   $978.05   $977.90