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 $71.53   7.276%   $76.7345   $76.73   $76.75   $76.70  
  Purchase #2 $139.78   10.421%   $154.3465   $154.35   $154.35   $154.30  
  Purchase #3 $75.33   8.496%   $81.73   $81.73   $81.75   $81.70  
  Purchase #4 $116.29   13.306%   $131.7635   $131.76   $131.75   $131.80  
  Purchase #5 $49.44   5.702%   $52.2591   $52.26   $52.25   $52.30  
  Purchase #6 $151.62   8.818%   $164.9899   $164.99   $165.00   $165.00  
  Purchase #7 $112.83   3.291%   $116.5432   $116.54   $116.55   $116.50  
  7 purchase totals = $716.82       $778.3667   $778.36   $778.40   $778.30