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 $248.50   5.694%   $262.6496   $262.65   $262.65   $262.60  
  Purchase #2 $142.85   11.247%   $158.9163   $158.92   $158.90   $158.90  
  Purchase #3 $161.93   11.576%   $180.675   $180.68   $180.70   $180.70  
  Purchase #4 $61.75   9.551%   $67.6477   $67.65   $67.65   $67.60  
  Purchase #5 $60.47   7.215%   $64.8329   $64.83   $64.85   $64.80  
  Purchase #6 $250.81   3.796%   $260.3307   $260.33   $260.35   $260.30  
  Purchase #7 $22.62   6.364%   $24.0595   $24.06   $24.05   $24.10  
  7 purchase totals = $948.93       $1,019.1117   $1,019.12   $1,019.15   $1,019.00