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 $57.39   4.466%   $59.953   $59.95   $59.95   $60.00  
  Purchase #2 $40.91   3.112%   $42.1831   $42.18   $42.20   $42.20  
  Purchase #3 $75.94   5.862%   $80.3916   $80.39   $80.40   $80.40  
  Purchase #4 $175.82   6.102%   $186.5485   $186.55   $186.55   $186.50  
  Purchase #5 $19.35   9.733%   $21.2333   $21.23   $21.25   $21.20  
  Purchase #6 $84.60   13.505%   $96.0252   $96.03   $96.05   $96.00  
  Purchase #7 $124.92   12.237%   $140.2065   $140.21   $140.20   $140.20  
  7 purchase totals = $578.93       $626.5412   $626.54   $626.60   $626.50