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 $235.55   13.473%   $267.2857   $267.29   $267.30   $267.30  
  Purchase #2 $83.82   3.425%   $86.6908   $86.69   $86.70   $86.70  
  Purchase #3 $190.33   11.214%   $211.6736   $211.67   $211.65   $211.70  
  Purchase #4 $233.46   13.601%   $265.2129   $265.21   $265.20   $265.20  
  Purchase #5 $176.76   4.741%   $185.1402   $185.14   $185.15   $185.10  
  Purchase #6 $173.42   5.872%   $183.6032   $183.60   $183.60   $183.60  
  Purchase #7 $236.96   5.551%   $250.1136   $250.11   $250.10   $250.10  
  7 purchase totals = $1,330.30       $1,449.7200   $1,449.71   $1,449.70   $1,449.70