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 $197.64   13.673%   $224.6633   $224.66   $224.65   $224.70  
  Purchase #2 $92.73   13.671%   $105.4071   $105.41   $105.40   $105.40  
  Purchase #3 $196.82   13.188%   $222.7766   $222.78   $222.80   $222.80  
  Purchase #4 $92.37   8.724%   $100.4284   $100.43   $100.45   $100.40  
  Purchase #5 $163.52   12.486%   $183.9371   $183.94   $183.95   $183.90  
  Purchase #6 $161.83   8.827%   $176.1147   $176.11   $176.10   $176.10  
  Purchase #7 $90.85   7.198%   $97.3894   $97.39   $97.40   $97.40  
  7 purchase totals = $995.76       $1,110.7166   $1,110.72   $1,110.75   $1,110.70