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 $230.67   11.463%   $257.1117   $257.11   $257.10   $257.10  
  Purchase #2 $227.71   9.590%   $249.5474   $249.55   $249.55   $249.50  
  Purchase #3 $87.38   8.634%   $94.9244   $94.92   $94.90   $94.90  
  Purchase #4 $74.25   12.571%   $83.584   $83.58   $83.60   $83.60  
  Purchase #5 $166.76   6.414%   $177.456   $177.46   $177.45   $177.50  
  Purchase #6 $65.72   11.209%   $73.0866   $73.09   $73.10   $73.10  
  Purchase #7 $15.37   9.833%   $16.8813   $16.88   $16.90   $16.90  
  7 purchase totals = $867.86       $952.5914   $952.59   $952.60   $952.60