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 $188.90   9.702%   $207.2271   $207.23   $207.25   $207.20  
  Purchase #2 $250.95   4.396%   $261.9818   $261.98   $262.00   $262.00  
  Purchase #3 $62.47   13.360%   $70.816   $70.82   $70.80   $70.80  
  Purchase #4 $161.72   4.843%   $169.5521   $169.55   $169.55   $169.60  
  Purchase #5 $222.51   13.351%   $252.2173   $252.22   $252.20   $252.20  
  Purchase #6 $125.55   6.179%   $133.3077   $133.31   $133.30   $133.30  
  Purchase #7 $7.61   13.704%   $8.6529   $8.65   $8.65   $8.70  
  7 purchase totals = $1,019.71       $1,103.7549   $1,103.76   $1,103.75   $1,103.80