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 $208.71   12.617%   $235.0429   $235.04   $235.05   $235.00  
  Purchase #2 $171.69   11.397%   $191.2575   $191.26   $191.25   $191.30  
  Purchase #3 $39.95   6.587%   $42.5815   $42.58   $42.60   $42.60  
  Purchase #4 $51.68   7.430%   $55.5198   $55.52   $55.50   $55.50  
  Purchase #5 $139.47   11.114%   $154.9707   $154.97   $154.95   $155.00  
  Purchase #6 $58.45   8.346%   $63.3282   $63.33   $63.35   $63.30  
  Purchase #7 $63.44   3.210%   $65.4764   $65.48   $65.50   $65.50  
  7 purchase totals = $733.39       $808.1770   $808.18   $808.20   $808.20