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 $131.61   6.663%   $140.3792   $140.38   $140.40   $140.40  
  Purchase #2 $245.36   13.573%   $278.6627   $278.66   $278.65   $278.70  
  Purchase #3 $109.61   6.819%   $117.0843   $117.08   $117.10   $117.10  
  Purchase #4 $226.91   8.646%   $246.5286   $246.53   $246.55   $246.50  
  Purchase #5 $207.63   8.203%   $224.6619   $224.66   $224.65   $224.70  
  Purchase #6 $180.81   5.841%   $191.3711   $191.37   $191.35   $191.40  
  Purchase #7 $60.96   5.392%   $64.247   $64.25   $64.25   $64.20  
  7 purchase totals = $1,162.89       $1,262.9348   $1,262.93   $1,262.95   $1,263.00