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 $205.26   13.792%   $233.5695   $233.57   $233.55   $233.60  
  Purchase #2 $203.63   13.531%   $231.1832   $231.18   $231.20   $231.20  
  Purchase #3 $51.77   4.152%   $53.9195   $53.92   $53.90   $53.90  
  Purchase #4 $235.29   7.397%   $252.6944   $252.69   $252.70   $252.70  
  Purchase #5 $203.53   11.339%   $226.6083   $226.61   $226.60   $226.60  
  Purchase #6 $101.74   11.587%   $113.5286   $113.53   $113.55   $113.50  
  Purchase #7 $208.71   9.311%   $228.143   $228.14   $228.15   $228.10  
  7 purchase totals = $1,209.93       $1,339.6465   $1,339.64   $1,339.65   $1,339.60