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 $52.44   13.480%   $59.5089   $59.51   $59.50   $59.50  
  Purchase #2 $249.51   3.378%   $257.9384   $257.94   $257.95   $257.90  
  Purchase #3 $250.93   4.623%   $262.5305   $262.53   $262.55   $262.50  
  Purchase #4 $72.77   3.193%   $75.0935   $75.09   $75.10   $75.10  
  Purchase #5 $33.86   4.868%   $35.5083   $35.51   $35.50   $35.50  
  Purchase #6 $46.98   6.233%   $49.9083   $49.91   $49.90   $49.90  
  Purchase #7 $194.59   12.688%   $219.2796   $219.28   $219.30   $219.30  
  7 purchase totals = $901.08       $959.7675   $959.77   $959.80   $959.70