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 $87.54   10.285%   $96.5435   $96.54   $96.55   $96.50  
  Purchase #2 $136.41   7.701%   $146.9149   $146.91   $146.90   $146.90  
  Purchase #3 $222.81   13.382%   $252.6264   $252.63   $252.65   $252.60  
  Purchase #4 $55.94   7.722%   $60.2597   $60.26   $60.25   $60.30  
  Purchase #5 $107.41   11.157%   $119.3937   $119.39   $119.40   $119.40  
  Purchase #6 $38.52   11.239%   $42.8493   $42.85   $42.85   $42.80  
  Purchase #7 $19.40   5.850%   $20.5349   $20.53   $20.55   $20.50  
  7 purchase totals = $668.03       $739.1224   $739.11   $739.15   $739.00