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 $49.68   12.579%   $55.9292   $55.93   $55.95   $55.90  
  Purchase #2 $179.43   3.518%   $185.7423   $185.74   $185.75   $185.70  
  Purchase #3 $80.51   7.624%   $86.6481   $86.65   $86.65   $86.60  
  Purchase #4 $201.67   6.410%   $214.597   $214.60   $214.60   $214.60  
  Purchase #5 $250.41   8.159%   $270.841   $270.84   $270.85   $270.80  
  Purchase #6 $184.50   9.628%   $202.2637   $202.26   $202.25   $202.30  
  Purchase #7 $245.75   7.119%   $263.2449   $263.24   $263.25   $263.20  
  7 purchase totals = $1,191.95       $1,279.2662   $1,279.26   $1,279.30   $1,279.10