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 $224.96   10.793%   $249.2399   $249.24   $249.25   $249.20  
  Purchase #2 $242.29   8.376%   $262.5842   $262.58   $262.60   $262.60  
  Purchase #3 $127.54   6.232%   $135.4883   $135.49   $135.50   $135.50  
  Purchase #4 $249.64   13.739%   $283.938   $283.94   $283.95   $283.90  
  Purchase #5 $53.85   7.110%   $57.6787   $57.68   $57.70   $57.70  
  Purchase #6 $11.78   5.274%   $12.4013   $12.40   $12.40   $12.40  
  Purchase #7 $49.83   9.869%   $54.7477   $54.75   $54.75   $54.70  
  7 purchase totals = $959.89       $1,056.0781   $1,056.08   $1,056.15   $1,056.00