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 $81.84   3.236%   $84.4883   $84.49   $84.50   $84.50  
  Purchase #2 $205.85   4.413%   $214.9342   $214.93   $214.95   $214.90  
  Purchase #3 $229.68   5.773%   $242.9394   $242.94   $242.95   $242.90  
  Purchase #4 $69.42   3.580%   $71.9052   $71.91   $71.90   $71.90  
  Purchase #5 $55.78   10.849%   $61.8316   $61.83   $61.85   $61.80  
  Purchase #6 $224.69   3.858%   $233.3585   $233.36   $233.35   $233.40  
  Purchase #7 $106.45   11.808%   $119.0196   $119.02   $119.00   $119.00  
  7 purchase totals = $973.71       $1,028.4768   $1,028.48   $1,028.50   $1,028.40