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 $167.62   5.357%   $176.5994   $176.60   $176.60   $176.60  
  Purchase #2 $83.39   13.482%   $94.6326   $94.63   $94.65   $94.60  
  Purchase #3 $32.58   11.410%   $36.2974   $36.30   $36.30   $36.30  
  Purchase #4 $164.36   6.771%   $175.4888   $175.49   $175.50   $175.50  
  Purchase #5 $132.29   5.808%   $139.9734   $139.97   $139.95   $140.00  
  Purchase #6 $64.46   7.730%   $69.4428   $69.44   $69.45   $69.40  
  Purchase #7 $79.70   6.788%   $85.11   $85.11   $85.10   $85.10  
  7 purchase totals = $724.40       $777.5444   $777.54   $777.55   $777.50