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 $168.94   4.788%   $177.0288   $177.03   $177.05   $177.00  
  Purchase #2 $244.71   13.614%   $278.0248   $278.02   $278.00   $278.00  
  Purchase #3 $164.69   3.623%   $170.6567   $170.66   $170.65   $170.70  
  Purchase #4 $102.33   12.196%   $114.8102   $114.81   $114.80   $114.80  
  Purchase #5 $219.78   12.834%   $247.9866   $247.99   $248.00   $248.00  
  Purchase #6 $75.59   12.241%   $84.843   $84.84   $84.85   $84.80  
  Purchase #7 $52.63   8.811%   $57.2672   $57.27   $57.25   $57.30  
  7 purchase totals = $1,028.67       $1,130.6173   $1,130.62   $1,130.60   $1,130.60