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 $23.97   7.743%   $25.826   $25.83   $25.85   $25.80  
  Purchase #2 $59.92   13.200%   $67.8294   $67.83   $67.85   $67.80  
  Purchase #3 $178.29   10.829%   $197.597   $197.60   $197.60   $197.60  
  Purchase #4 $67.49   12.693%   $76.0565   $76.06   $76.05   $76.10  
  Purchase #5 $11.55   9.777%   $12.6792   $12.68   $12.70   $12.70  
  Purchase #6 $218.44   3.567%   $226.2318   $226.23   $226.25   $226.20  
  Purchase #7 $17.29   6.277%   $18.3753   $18.38   $18.40   $18.40  
  7 purchase totals = $576.95       $624.5952   $624.61   $624.70   $624.60