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 $118.59   6.773%   $126.6221   $126.62   $126.60   $126.60  
  Purchase #2 $9.49   8.321%   $10.2797   $10.28   $10.30   $10.30  
  Purchase #3 $47.41   8.524%   $51.4512   $51.45   $51.45   $51.50  
  Purchase #4 $69.61   6.787%   $74.3344   $74.33   $74.35   $74.30  
  Purchase #5 $69.35   11.688%   $77.4556   $77.46   $77.45   $77.50  
  Purchase #6 $26.31   11.647%   $29.3743   $29.37   $29.35   $29.40  
  Purchase #7 $215.43   5.260%   $226.7616   $226.76   $226.75   $226.80  
  7 purchase totals = $556.19       $596.2789   $596.27   $596.25   $596.40