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 $122.48   3.217%   $126.4202   $126.42   $126.40   $126.40  
  Purchase #2 $248.27   5.131%   $261.0087   $261.01   $261.00   $261.00  
  Purchase #3 $38.75   5.277%   $40.7948   $40.79   $40.80   $40.80  
  Purchase #4 $141.93   13.538%   $161.1445   $161.14   $161.15   $161.10  
  Purchase #5 $140.89   7.753%   $151.8132   $151.81   $151.80   $151.80  
  Purchase #6 $59.89   3.789%   $62.1592   $62.16   $62.15   $62.20  
  Purchase #7 $153.88   7.660%   $165.6672   $165.67   $165.65   $165.70  
  7 purchase totals = $906.09       $969.0078   $969.00   $968.95   $969.00