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 $186.36   11.582%   $207.9442   $207.94   $207.95   $207.90  
  Purchase #2 $68.68   9.749%   $75.3756   $75.38   $75.40   $75.40  
  Purchase #3 $136.93   4.373%   $142.9179   $142.92   $142.90   $142.90  
  Purchase #4 $211.51   11.800%   $236.4682   $236.47   $236.45   $236.50  
  Purchase #5 $54.64   4.157%   $56.9114   $56.91   $56.90   $56.90  
  Purchase #6 $113.80   5.378%   $119.9202   $119.92   $119.90   $119.90  
  Purchase #7 $222.47   9.724%   $244.103   $244.10   $244.10   $244.10  
  7 purchase totals = $994.39       $1,083.6405   $1,083.64   $1,083.60   $1,083.60