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 $234.81   5.647%   $248.0697   $248.07   $248.05   $248.10  
  Purchase #2 $249.38   3.723%   $258.6644   $258.66   $258.65   $258.70  
  Purchase #3 $210.93   8.458%   $228.7705   $228.77   $228.75   $228.80  
  Purchase #4 $185.76   10.672%   $205.5843   $205.58   $205.60   $205.60  
  Purchase #5 $232.64   5.533%   $245.512   $245.51   $245.50   $245.50  
  Purchase #6 $81.69   10.804%   $90.5158   $90.52   $90.50   $90.50  
  Purchase #7 $200.41   9.161%   $218.7696   $218.77   $218.75   $218.80  
  7 purchase totals = $1,395.62       $1,495.8863   $1,495.88   $1,495.80   $1,496.00