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 $115.68   3.686%   $119.944   $119.94   $119.95   $119.90  
  Purchase #2 $224.41   13.266%   $254.1802   $254.18   $254.20   $254.20  
  Purchase #3 $71.93   3.643%   $74.5504   $74.55   $74.55   $74.60  
  Purchase #4 $222.71   12.247%   $249.9853   $249.99   $250.00   $250.00  
  Purchase #5 $131.76   7.223%   $141.277   $141.28   $141.30   $141.30  
  Purchase #6 $77.31   11.414%   $86.1342   $86.13   $86.15   $86.10  
  Purchase #7 $100.36   6.809%   $107.1935   $107.19   $107.20   $107.20  
  7 purchase totals = $944.16       $1,033.2646   $1,033.26   $1,033.35   $1,033.30