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 $249.52   6.829%   $266.5597   $266.56   $266.55   $266.60  
  Purchase #2 $213.88   5.688%   $226.0455   $226.05   $226.05   $226.00  
  Purchase #3 $154.76   3.813%   $160.661   $160.66   $160.65   $160.70  
  Purchase #4 $101.77   12.619%   $114.6124   $114.61   $114.60   $114.60  
  Purchase #5 $195.59   13.758%   $222.4993   $222.50   $222.50   $222.50  
  Purchase #6 $189.70   12.307%   $213.0464   $213.05   $213.05   $213.00  
  Purchase #7 $30.39   11.259%   $33.8116   $33.81   $33.80   $33.80  
  7 purchase totals = $1,135.61       $1,237.2359   $1,237.24   $1,237.20   $1,237.20