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 $54.34   12.871%   $61.3341   $61.33   $61.35   $61.30  
  Purchase #2 $245.75   3.191%   $253.5919   $253.59   $253.60   $253.60  
  Purchase #3 $54.27   7.846%   $58.528   $58.53   $58.55   $58.50  
  Purchase #4 $236.95   6.598%   $252.584   $252.58   $252.60   $252.60  
  Purchase #5 $119.41   8.332%   $129.3592   $129.36   $129.35   $129.40  
  Purchase #6 $179.71   9.607%   $196.9747   $196.97   $196.95   $197.00  
  Purchase #7 $249.61   7.725%   $268.8924   $268.89   $268.90   $268.90  
  7 purchase totals = $1,140.04       $1,221.2643   $1,221.25   $1,221.30   $1,221.30