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 $179.47   8.662%   $195.0157   $195.02   $195.00   $195.00  
  Purchase #2 $23.72   10.849%   $26.2934   $26.29   $26.30   $26.30  
  Purchase #3 $89.30   8.503%   $96.8932   $96.89   $96.90   $96.90  
  Purchase #4 $52.48   12.734%   $59.1628   $59.16   $59.15   $59.20  
  Purchase #5 $177.58   11.215%   $197.4956   $197.50   $197.50   $197.50  
  Purchase #6 $17.81   13.609%   $20.2338   $20.23   $20.25   $20.20  
  Purchase #7 $181.87   9.848%   $199.7806   $199.78   $199.80   $199.80  
  7 purchase totals = $722.23       $794.8751   $794.87   $794.90   $794.90