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 $243.88   10.520%   $269.5362   $269.54   $269.55   $269.50  
  Purchase #2 $48.50   11.430%   $54.0436   $54.04   $54.05   $54.00  
  Purchase #3 $174.74   5.426%   $184.2214   $184.22   $184.20   $184.20  
  Purchase #4 $250.25   4.607%   $261.779   $261.78   $261.80   $261.80  
  Purchase #5 $93.92   4.411%   $98.0628   $98.06   $98.05   $98.10  
  Purchase #6 $79.59   10.472%   $87.9247   $87.92   $87.90   $87.90  
  Purchase #7 $162.66   13.473%   $184.5752   $184.58   $184.60   $184.60  
  7 purchase totals = $1,053.54       $1,140.1429   $1,140.14   $1,140.15   $1,140.10