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 $49.65   6.357%   $52.8063   $52.81   $52.80   $52.80  
  Purchase #2 $53.99   4.183%   $56.2484   $56.25   $56.25   $56.20  
  Purchase #3 $176.33   5.693%   $186.3685   $186.37   $186.35   $186.40  
  Purchase #4 $220.28   3.318%   $227.5889   $227.59   $227.60   $227.60  
  Purchase #5 $167.61   3.798%   $173.9758   $173.98   $174.00   $174.00  
  Purchase #6 $157.81   13.573%   $179.2296   $179.23   $179.25   $179.20  
  Purchase #7 $239.85   11.601%   $267.675   $267.68   $267.70   $267.70  
  7 purchase totals = $1,065.52       $1,143.8925   $1,143.91   $1,143.95   $1,143.90