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 $211.90   8.137%   $229.1423   $229.14   $229.15   $229.10  
  Purchase #2 $248.34   5.520%   $262.0484   $262.05   $262.05   $262.00  
  Purchase #3 $229.47   12.526%   $258.2134   $258.21   $258.20   $258.20  
  Purchase #4 $44.39   3.542%   $45.9623   $45.96   $45.95   $46.00  
  Purchase #5 $229.37   8.432%   $248.7105   $248.71   $248.70   $248.70  
  Purchase #6 $168.37   7.145%   $180.4   $180.40   $180.40   $180.40  
  Purchase #7 $121.72   9.425%   $133.1921   $133.19   $133.20   $133.20  
  7 purchase totals = $1,253.56       $1,357.6690   $1,357.66   $1,357.65   $1,357.60