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 $204.77   5.671%   $216.3825   $216.38   $216.40   $216.40  
  Purchase #2 $233.50   12.137%   $261.8399   $261.84   $261.85   $261.80  
  Purchase #3 $155.97   12.513%   $175.4865   $175.49   $175.50   $175.50  
  Purchase #4 $249.83   3.371%   $258.2518   $258.25   $258.25   $258.30  
  Purchase #5 $202.44   11.413%   $225.5445   $225.54   $225.55   $225.50  
  Purchase #6 $8.28   4.619%   $8.6625   $8.66   $8.65   $8.70  
  Purchase #7 $143.69   10.454%   $158.7114   $158.71   $158.70   $158.70  
  7 purchase totals = $1,198.48       $1,304.8791   $1,304.87   $1,304.90   $1,304.90