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 $180.27   12.574%   $202.9371   $202.94   $202.95   $202.90  
  Purchase #2 $187.78   9.452%   $205.529   $205.53   $205.55   $205.50  
  Purchase #3 $109.86   3.413%   $113.6095   $113.61   $113.60   $113.60  
  Purchase #4 $46.45   8.484%   $50.3908   $50.39   $50.40   $50.40  
  Purchase #5 $206.74   11.850%   $231.2387   $231.24   $231.25   $231.20  
  Purchase #6 $174.82   7.134%   $187.2917   $187.29   $187.30   $187.30  
  Purchase #7 $209.41   12.724%   $236.0553   $236.06   $236.05   $236.10  
  7 purchase totals = $1,115.33       $1,227.0521   $1,227.06   $1,227.10   $1,227.00