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 $204.62   5.190%   $215.2398   $215.24   $215.25   $215.20  
  Purchase #2 $230.69   5.603%   $243.6156   $243.62   $243.60   $243.60  
  Purchase #3 $195.42   4.737%   $204.677   $204.68   $204.70   $204.70  
  Purchase #4 $125.83   12.542%   $141.6116   $141.61   $141.60   $141.60  
  Purchase #5 $173.37   9.824%   $190.4019   $190.40   $190.40   $190.40  
  Purchase #6 $121.27   5.266%   $127.6561   $127.66   $127.65   $127.70  
  Purchase #7 $143.88   9.297%   $157.2565   $157.26   $157.25   $157.30  
  7 purchase totals = $1,195.08       $1,280.4585   $1,280.47   $1,280.45   $1,280.50