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 $113.99   11.847%   $127.4944   $127.49   $127.50   $127.50  
  Purchase #2 $228.87   3.413%   $236.6813   $236.68   $236.70   $236.70  
  Purchase #3 $94.56   11.207%   $105.1573   $105.16   $105.15   $105.20  
  Purchase #4 $134.86   9.183%   $147.2442   $147.24   $147.25   $147.20  
  Purchase #5 $227.71   11.719%   $254.3953   $254.40   $254.40   $254.40  
  Purchase #6 $188.88   8.780%   $205.4637   $205.46   $205.45   $205.50  
  Purchase #7 $190.53   7.807%   $205.4047   $205.40   $205.40   $205.40  
  7 purchase totals = $1,179.40       $1,281.8409   $1,281.83   $1,281.85   $1,281.90