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 $110.47   13.524%   $125.41   $125.41   $125.40   $125.40  
  Purchase #2 $169.39   5.687%   $179.0232   $179.02   $179.00   $179.00  
  Purchase #3 $60.68   11.685%   $67.7705   $67.77   $67.75   $67.80  
  Purchase #4 $236.55   11.724%   $264.2831   $264.28   $264.30   $264.30  
  Purchase #5 $86.97   4.459%   $90.848   $90.85   $90.85   $90.80  
  Purchase #6 $226.88   9.768%   $249.0416   $249.04   $249.05   $249.00  
  Purchase #7 $95.64   7.307%   $102.6284   $102.63   $102.65   $102.60  
  7 purchase totals = $986.58       $1,079.0048   $1,079.00   $1,079.00   $1,078.90