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 $238.47   10.386%   $263.2375   $263.24   $263.25   $263.20  
  Purchase #2 $33.83   5.522%   $35.6981   $35.70   $35.70   $35.70  
  Purchase #3 $73.69   10.704%   $81.5778   $81.58   $81.60   $81.60  
  Purchase #4 $235.34   5.863%   $249.138   $249.14   $249.15   $249.10  
  Purchase #5 $181.61   8.613%   $197.2521   $197.25   $197.25   $197.30  
  Purchase #6 $54.52   11.372%   $60.72   $60.72   $60.70   $60.70  
  Purchase #7 $58.58   11.843%   $65.5176   $65.52   $65.50   $65.50  
  7 purchase totals = $876.04       $953.1411   $953.15   $953.15   $953.10