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 $160.73   4.460%   $167.8986   $167.90   $167.90   $167.90  
  Purchase #2 $227.92   4.210%   $237.5154   $237.52   $237.50   $237.50  
  Purchase #3 $183.90   5.416%   $193.86   $193.86   $193.85   $193.90  
  Purchase #4 $119.73   6.269%   $127.2359   $127.24   $127.25   $127.20  
  Purchase #5 $243.88   7.191%   $261.4174   $261.42   $261.40   $261.40  
  Purchase #6 $224.37   3.469%   $232.1534   $232.15   $232.15   $232.20  
  Purchase #7 $140.69   3.340%   $145.389   $145.39   $145.40   $145.40  
  7 purchase totals = $1,301.22       $1,365.4697   $1,365.48   $1,365.45   $1,365.50