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 $52.56   12.699%   $59.2346   $59.23   $59.25   $59.20  
  Purchase #2 $88.80   10.360%   $97.9997   $98.00   $98.00   $98.00  
  Purchase #3 $178.88   13.622%   $203.247   $203.25   $203.25   $203.20  
  Purchase #4 $39.46   7.725%   $42.5083   $42.51   $42.50   $42.50  
  Purchase #5 $194.89   6.235%   $207.0414   $207.04   $207.05   $207.00  
  Purchase #6 $123.81   3.506%   $128.1508   $128.15   $128.15   $128.20  
  Purchase #7 $144.76   13.189%   $163.8524   $163.85   $163.85   $163.90  
  7 purchase totals = $823.16       $902.0342   $902.03   $902.05   $902.00