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 $207.33   13.619%   $235.5663   $235.57   $235.55   $235.60  
  Purchase #2 $220.39   13.646%   $250.4644   $250.46   $250.45   $250.50  
  Purchase #3 $167.86   9.176%   $183.2628   $183.26   $183.25   $183.30  
  Purchase #4 $226.44   5.751%   $239.4626   $239.46   $239.45   $239.50  
  Purchase #5 $49.91   11.411%   $55.6052   $55.61   $55.60   $55.60  
  Purchase #6 $194.48   3.781%   $201.8333   $201.83   $201.85   $201.80  
  Purchase #7 $146.40   9.445%   $160.2275   $160.23   $160.25   $160.20  
  7 purchase totals = $1,212.81       $1,326.4221   $1,326.42   $1,326.40   $1,326.50