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 $224.76   11.798%   $251.2772   $251.28   $251.30   $251.30  
  Purchase #2 $208.47   9.144%   $227.5325   $227.53   $227.55   $227.50  
  Purchase #3 $213.45   6.175%   $226.6305   $226.63   $226.65   $226.60  
  Purchase #4 $172.57   8.158%   $186.6483   $186.65   $186.65   $186.60  
  Purchase #5 $249.34   13.604%   $283.2602   $283.26   $283.25   $283.30  
  Purchase #6 $21.65   13.715%   $24.6193   $24.62   $24.60   $24.60  
  Purchase #7 $214.39   8.832%   $233.3249   $233.32   $233.30   $233.30  
  7 purchase totals = $1,304.63       $1,433.2929   $1,433.29   $1,433.30   $1,433.20