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 $49.66   13.290%   $56.2598   $56.26   $56.25   $56.30  
  Purchase #2 $113.96   8.106%   $123.1976   $123.20   $123.20   $123.20  
  Purchase #3 $40.61   4.591%   $42.4744   $42.47   $42.45   $42.50  
  Purchase #4 $179.49   3.794%   $186.2999   $186.30   $186.30   $186.30  
  Purchase #5 $210.45   6.541%   $224.2155   $224.22   $224.20   $224.20  
  Purchase #6 $230.81   6.679%   $246.2258   $246.23   $246.25   $246.20  
  Purchase #7 $127.81   8.365%   $138.5013   $138.50   $138.50   $138.50  
  7 purchase totals = $952.79       $1,017.1743   $1,017.18   $1,017.15   $1,017.20