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 $227.43   5.792%   $240.6027   $240.60   $240.60   $240.60  
  Purchase #2 $162.71   10.417%   $179.6595   $179.66   $179.65   $179.70  
  Purchase #3 $233.47   6.542%   $248.7436   $248.74   $248.75   $248.70  
  Purchase #4 $246.73   8.662%   $268.1018   $268.10   $268.10   $268.10  
  Purchase #5 $69.76   10.835%   $77.3185   $77.32   $77.30   $77.30  
  Purchase #6 $53.53   12.746%   $60.3529   $60.35   $60.35   $60.40  
  Purchase #7 $76.59   13.462%   $86.9005   $86.90   $86.90   $86.90  
  7 purchase totals = $1,070.22       $1,161.6795   $1,161.67   $1,161.65   $1,161.70