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 $67.98   10.671%   $75.2341   $75.23   $75.25   $75.20  
  Purchase #2 $57.95   12.600%   $65.2517   $65.25   $65.25   $65.30  
  Purchase #3 $250.88   3.708%   $260.1826   $260.18   $260.20   $260.20  
  Purchase #4 $112.44   6.839%   $120.1298   $120.13   $120.15   $120.10  
  Purchase #5 $232.29   12.370%   $261.0243   $261.02   $261.00   $261.00  
  Purchase #6 $156.92   5.569%   $165.6589   $165.66   $165.65   $165.70  
  Purchase #7 $75.29   7.745%   $81.1212   $81.12   $81.10   $81.10  
  7 purchase totals = $953.75       $1,028.6026   $1,028.59   $1,028.60   $1,028.60