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 $43.99   13.543%   $49.9476   $49.95   $49.95   $49.90  
  Purchase #2 $146.76   13.618%   $166.7458   $166.75   $166.75   $166.70  
  Purchase #3 $179.71   7.105%   $192.4784   $192.48   $192.50   $192.50  
  Purchase #4 $224.60   4.620%   $234.9765   $234.98   $235.00   $235.00  
  Purchase #5 $135.39   7.619%   $145.7054   $145.71   $145.70   $145.70  
  Purchase #6 $242.74   6.204%   $257.7996   $257.80   $257.80   $257.80  
  Purchase #7 $82.36   4.328%   $85.9245   $85.92   $85.90   $85.90  
  7 purchase totals = $1,055.55       $1,133.5778   $1,133.59   $1,133.60   $1,133.50