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 $177.27   12.401%   $199.2533   $199.25   $199.25   $199.30  
  Purchase #2 $38.61   7.387%   $41.4621   $41.46   $41.45   $41.50  
  Purchase #3 $158.69   12.197%   $178.0454   $178.05   $178.05   $178.00  
  Purchase #4 $75.97   7.240%   $81.4702   $81.47   $81.45   $81.50  
  Purchase #5 $190.93   12.141%   $214.1108   $214.11   $214.10   $214.10  
  Purchase #6 $182.89   12.558%   $205.8573   $205.86   $205.85   $205.90  
  Purchase #7 $127.59   6.716%   $136.1589   $136.16   $136.15   $136.20  
  7 purchase totals = $951.95       $1,056.3580   $1,056.36   $1,056.30   $1,056.50