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 $162.77   13.514%   $184.7667   $184.77   $184.75   $184.80  
  Purchase #2 $115.83   8.724%   $125.935   $125.94   $125.95   $125.90  
  Purchase #3 $74.69   7.339%   $80.1715   $80.17   $80.15   $80.20  
  Purchase #4 $26.94   4.577%   $28.173   $28.17   $28.15   $28.20  
  Purchase #5 $70.65   7.592%   $76.0137   $76.01   $76.00   $76.00  
  Purchase #6 $182.26   8.444%   $197.65   $197.65   $197.65   $197.70  
  Purchase #7 $123.70   13.106%   $139.9121   $139.91   $139.90   $139.90  
  7 purchase totals = $756.84       $832.6220   $832.62   $832.55   $832.70