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 $187.63   5.858%   $198.6214   $198.62   $198.60   $198.60  
  Purchase #2 $95.99   3.864%   $99.6991   $99.70   $99.70   $99.70  
  Purchase #3 $25.82   9.320%   $28.2264   $28.23   $28.25   $28.20  
  Purchase #4 $54.70   4.240%   $57.0193   $57.02   $57.00   $57.00  
  Purchase #5 $26.46   9.667%   $29.0179   $29.02   $29.00   $29.00  
  Purchase #6 $21.98   6.604%   $23.4316   $23.43   $23.45   $23.40  
  Purchase #7 $242.29   8.149%   $262.0342   $262.03   $262.05   $262.00  
  7 purchase totals = $654.87       $698.0499   $698.05   $698.05   $697.90