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 $154.51   6.639%   $164.7679   $164.77   $164.75   $164.80  
  Purchase #2 $167.41   11.487%   $186.6404   $186.64   $186.65   $186.60  
  Purchase #3 $198.93   9.719%   $218.264   $218.26   $218.25   $218.30  
  Purchase #4 $243.61   5.874%   $257.9197   $257.92   $257.90   $257.90  
  Purchase #5 $201.78   13.769%   $229.5631   $229.56   $229.55   $229.60  
  Purchase #6 $151.54   8.104%   $163.8208   $163.82   $163.80   $163.80  
  Purchase #7 $247.26   3.509%   $255.9364   $255.94   $255.95   $255.90  
  7 purchase totals = $1,365.04       $1,476.9123   $1,476.91   $1,476.85   $1,476.90