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 $204.68   10.396%   $225.9585   $225.96   $225.95   $226.00  
  Purchase #2 $137.77   3.194%   $142.1704   $142.17   $142.15   $142.20  
  Purchase #3 $130.87   4.437%   $136.6767   $136.68   $136.70   $136.70  
  Purchase #4 $152.82   12.209%   $171.4778   $171.48   $171.50   $171.50  
  Purchase #5 $174.83   12.574%   $196.8131   $196.81   $196.80   $196.80  
  Purchase #6 $114.35   11.762%   $127.7998   $127.80   $127.80   $127.80  
  Purchase #7 $23.89   10.509%   $26.4006   $26.40   $26.40   $26.40  
  7 purchase totals = $939.21       $1,027.2969   $1,027.30   $1,027.30   $1,027.40