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 $24.43   10.427%   $26.9773   $26.98   $27.00   $27.00  
  Purchase #2 $61.87   4.338%   $64.5539   $64.55   $64.55   $64.60  
  Purchase #3 $190.52   8.196%   $206.135   $206.14   $206.15   $206.10  
  Purchase #4 $59.37   3.134%   $61.2307   $61.23   $61.25   $61.20  
  Purchase #5 $151.93   3.126%   $156.6793   $156.68   $156.70   $156.70  
  Purchase #6 $238.47   9.685%   $261.5658   $261.57   $261.55   $261.60  
  Purchase #7 $219.32   13.290%   $248.4676   $248.47   $248.45   $248.50  
  7 purchase totals = $945.91       $1,025.6096   $1,025.62   $1,025.65   $1,025.70