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 $239.99   9.563%   $262.9402   $262.94   $262.95   $262.90  
  Purchase #2 $48.81   6.541%   $52.0027   $52.00   $52.00   $52.00  
  Purchase #3 $237.32   5.669%   $250.7737   $250.77   $250.75   $250.80  
  Purchase #4 $153.64   8.547%   $166.7716   $166.77   $166.75   $166.80  
  Purchase #5 $203.33   5.852%   $215.2289   $215.23   $215.25   $215.20  
  Purchase #6 $96.89   11.445%   $107.9791   $107.98   $108.00   $108.00  
  Purchase #7 $52.58   9.216%   $57.4258   $57.43   $57.45   $57.40  
  7 purchase totals = $1,032.56       $1,113.1220   $1,113.12   $1,113.15   $1,113.10