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 $227.33   9.673%   $249.3196   $249.32   $249.30   $249.30  
  Purchase #2 $37.55   8.344%   $40.6832   $40.68   $40.70   $40.70  
  Purchase #3 $105.88   3.263%   $109.3349   $109.33   $109.35   $109.30  
  Purchase #4 $41.64   5.830%   $44.0676   $44.07   $44.05   $44.10  
  Purchase #5 $241.76   13.718%   $274.9246   $274.92   $274.90   $274.90  
  Purchase #6 $112.64   5.845%   $119.2238   $119.22   $119.20   $119.20  
  Purchase #7 $220.78   4.241%   $230.1433   $230.14   $230.15   $230.10  
  7 purchase totals = $987.58       $1,067.6970   $1,067.68   $1,067.65   $1,067.60