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 $239.42   12.611%   $269.6133   $269.61   $269.60   $269.60  
  Purchase #2 $51.79   3.500%   $53.6027   $53.60   $53.60   $53.60  
  Purchase #3 $128.51   5.598%   $135.704   $135.70   $135.70   $135.70  
  Purchase #4 $247.83   4.402%   $258.7395   $258.74   $258.75   $258.70  
  Purchase #5 $184.79   12.465%   $207.8241   $207.82   $207.80   $207.80  
  Purchase #6 $72.78   7.704%   $78.387   $78.39   $78.40   $78.40  
  Purchase #7 $45.30   9.703%   $49.6955   $49.70   $49.70   $49.70  
  7 purchase totals = $970.42       $1,053.5661   $1,053.56   $1,053.55   $1,053.50