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 $247.81   11.733%   $276.8855   $276.89   $276.90   $276.90  
  Purchase #2 $44.32   13.134%   $50.141   $50.14   $50.15   $50.10  
  Purchase #3 $191.43   9.108%   $208.8654   $208.87   $208.85   $208.90  
  Purchase #4 $26.39   8.376%   $28.6004   $28.60   $28.60   $28.60  
  Purchase #5 $219.78   5.228%   $231.2701   $231.27   $231.25   $231.30  
  Purchase #6 $96.33   5.786%   $101.9037   $101.90   $101.90   $101.90  
  Purchase #7 $115.26   9.653%   $126.386   $126.39   $126.40   $126.40  
  7 purchase totals = $941.32       $1,024.0521   $1,024.06   $1,024.05   $1,024.10