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 $161.63   12.806%   $182.3283   $182.33   $182.35   $182.30  
  Purchase #2 $119.75   11.531%   $133.5584   $133.56   $133.55   $133.60  
  Purchase #3 $18.77   12.382%   $21.0941   $21.09   $21.10   $21.10  
  Purchase #4 $194.67   6.278%   $206.8914   $206.89   $206.90   $206.90  
  Purchase #5 $133.70   8.284%   $144.7757   $144.78   $144.80   $144.80  
  Purchase #6 $125.46   6.567%   $133.699   $133.70   $133.70   $133.70  
  Purchase #7 $234.43   9.432%   $256.5414   $256.54   $256.55   $256.50  
  7 purchase totals = $988.41       $1,078.8883   $1,078.89   $1,078.95   $1,078.90