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 $214.32   12.586%   $241.2943   $241.29   $241.30   $241.30  
  Purchase #2 $113.60   3.618%   $117.71   $117.71   $117.70   $117.70  
  Purchase #3 $225.62   7.260%   $242   $242.00   $242.00   $242.00  
  Purchase #4 $206.98   4.311%   $215.9029   $215.90   $215.90   $215.90  
  Purchase #5 $119.62   9.507%   $130.9923   $130.99   $131.00   $131.00  
  Purchase #6 $232.30   8.262%   $251.4926   $251.49   $251.50   $251.50  
  Purchase #7 $49.78   8.444%   $53.9834   $53.98   $54.00   $54.00  
  7 purchase totals = $1,162.22       $1,253.3755   $1,253.36   $1,253.40   $1,253.40