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 $24.51   6.104%   $26.0061   $26.01   $26.00   $26.00  
  Purchase #2 $133.27   4.576%   $139.3684   $139.37   $139.35   $139.40  
  Purchase #3 $146.88   10.517%   $162.3274   $162.33   $162.35   $162.30  
  Purchase #4 $23.74   7.732%   $25.5756   $25.58   $25.60   $25.60  
  Purchase #5 $221.50   8.743%   $240.8657   $240.87   $240.85   $240.90  
  Purchase #6 $166.63   11.487%   $185.7708   $185.77   $185.75   $185.80  
  Purchase #7 $231.55   10.724%   $256.3814   $256.38   $256.40   $256.40  
  7 purchase totals = $948.08       $1,036.2954   $1,036.31   $1,036.30   $1,036.40