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 $55.46   10.269%   $61.1552   $61.16   $61.15   $61.20  
  Purchase #2 $226.92   9.362%   $248.1643   $248.16   $248.15   $248.20  
  Purchase #3 $69.56   5.378%   $73.3009   $73.30   $73.30   $73.30  
  Purchase #4 $55.82   3.439%   $57.7396   $57.74   $57.75   $57.70  
  Purchase #5 $26.77   6.350%   $28.4699   $28.47   $28.45   $28.50  
  Purchase #6 $13.52   7.130%   $14.484   $14.48   $14.50   $14.50  
  Purchase #7 $247.51   5.833%   $261.9473   $261.95   $261.95   $261.90  
  7 purchase totals = $695.56       $745.2612   $745.26   $745.25   $745.30