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 $69.73   9.830%   $76.5845   $76.58   $76.60   $76.60  
  Purchase #2 $183.49   5.713%   $193.9728   $193.97   $193.95   $194.00  
  Purchase #3 $44.43   7.694%   $47.8484   $47.85   $47.85   $47.80  
  Purchase #4 $166.75   3.138%   $171.9826   $171.98   $172.00   $172.00  
  Purchase #5 $147.74   5.440%   $155.7771   $155.78   $155.80   $155.80  
  Purchase #6 $142.75   13.102%   $161.4531   $161.45   $161.45   $161.50  
  Purchase #7 $145.28   13.359%   $164.688   $164.69   $164.70   $164.70  
  7 purchase totals = $900.17       $972.3065   $972.30   $972.35   $972.40