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 $216.90   10.564%   $239.8133   $239.81   $239.80   $239.80  
  Purchase #2 $187.68   9.522%   $205.5509   $205.55   $205.55   $205.60  
  Purchase #3 $242.64   12.373%   $272.6618   $272.66   $272.65   $272.70  
  Purchase #4 $236.44   8.518%   $256.58   $256.58   $256.60   $256.60  
  Purchase #5 $205.64   10.813%   $227.8759   $227.88   $227.90   $227.90  
  Purchase #6 $141.91   13.122%   $160.5314   $160.53   $160.55   $160.50  
  Purchase #7 $132.26   7.305%   $141.9216   $141.92   $141.90   $141.90  
  7 purchase totals = $1,363.47       $1,504.9349   $1,504.93   $1,504.95   $1,505.00