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 $152.80   5.162%   $160.6875   $160.69   $160.70   $160.70  
  Purchase #2 $177.51   3.493%   $183.7104   $183.71   $183.70   $183.70  
  Purchase #3 $103.96   3.451%   $107.5477   $107.55   $107.55   $107.50  
  Purchase #4 $217.51   3.333%   $224.7596   $224.76   $224.75   $224.80  
  Purchase #5 $54.60   4.263%   $56.9276   $56.93   $56.95   $56.90  
  Purchase #6 $157.31   4.523%   $164.4251   $164.43   $164.45   $164.40  
  Purchase #7 $50.82   3.271%   $52.4823   $52.48   $52.50   $52.50  
  7 purchase totals = $914.51       $950.5402   $950.55   $950.60   $950.50