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 $243.93   10.628%   $269.8549   $269.85   $269.85   $269.90  
  Purchase #2 $124.65   6.189%   $132.3646   $132.36   $132.35   $132.40  
  Purchase #3 $241.32   5.262%   $254.0183   $254.02   $254.00   $254.00  
  Purchase #4 $63.42   5.234%   $66.7394   $66.74   $66.75   $66.70  
  Purchase #5 $23.90   8.856%   $26.0166   $26.02   $26.00   $26.00  
  Purchase #6 $27.33   9.779%   $30.0026   $30.00   $30.00   $30.00  
  Purchase #7 $170.26   7.324%   $182.7298   $182.73   $182.75   $182.70  
  7 purchase totals = $894.81       $961.7262   $961.72   $961.70   $961.70