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 $101.95   13.421%   $115.6327   $115.63   $115.65   $115.60  
  Purchase #2 $61.65   8.793%   $67.0709   $67.07   $67.05   $67.10  
  Purchase #3 $115.39   7.836%   $124.432   $124.43   $124.45   $124.40  
  Purchase #4 $46.82   3.798%   $48.5982   $48.60   $48.60   $48.60  
  Purchase #5 $80.31   8.684%   $87.2841   $87.28   $87.30   $87.30  
  Purchase #6 $89.54   12.747%   $100.9537   $100.95   $100.95   $101.00  
  Purchase #7 $238.28   9.834%   $261.7125   $261.71   $261.70   $261.70  
  7 purchase totals = $733.94       $805.6841   $805.67   $805.70   $805.70