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 $67.55   13.591%   $76.7307   $76.73   $76.75   $76.70  
  Purchase #2 $176.81   4.316%   $184.4411   $184.44   $184.45   $184.40  
  Purchase #3 $97.94   7.458%   $105.2444   $105.24   $105.25   $105.20  
  Purchase #4 $64.96   7.499%   $69.8314   $69.83   $69.85   $69.80  
  Purchase #5 $41.69   11.361%   $46.4264   $46.43   $46.45   $46.40  
  Purchase #6 $233.79   7.357%   $250.9899   $250.99   $251.00   $251.00  
  Purchase #7 $117.37   5.209%   $123.4838   $123.48   $123.50   $123.50  
  7 purchase totals = $800.11       $857.1477   $857.14   $857.25   $857.00