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 $136.91   12.542%   $154.0813   $154.08   $154.10   $154.10  
  Purchase #2 $23.68   3.624%   $24.5382   $24.54   $24.55   $24.50  
  Purchase #3 $153.41   12.151%   $172.0508   $172.05   $172.05   $172.10  
  Purchase #4 $214.46   11.868%   $239.9121   $239.91   $239.90   $239.90  
  Purchase #5 $207.65   12.332%   $233.2574   $233.26   $233.25   $233.30  
  Purchase #6 $241.68   4.843%   $253.3846   $253.38   $253.40   $253.40  
  Purchase #7 $238.73   11.291%   $265.685   $265.69   $265.70   $265.70  
  7 purchase totals = $1,216.52       $1,342.9094   $1,342.91   $1,342.95   $1,343.00