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 $186.99   10.140%   $205.9508   $205.95   $205.95   $206.00  
  Purchase #2 $197.82   4.214%   $206.1561   $206.16   $206.15   $206.20  
  Purchase #3 $68.36   4.870%   $71.6891   $71.69   $71.70   $71.70  
  Purchase #4 $214.35   11.579%   $239.1696   $239.17   $239.15   $239.20  
  Purchase #5 $71.81   9.750%   $78.8115   $78.81   $78.80   $78.80  
  Purchase #6 $241.36   4.779%   $252.8946   $252.89   $252.90   $252.90  
  Purchase #7 $164.73   13.164%   $186.4151   $186.42   $186.40   $186.40  
  7 purchase totals = $1,145.42       $1,241.0868   $1,241.09   $1,241.05   $1,241.20