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 $226.87   10.182%   $249.9699   $249.97   $249.95   $250.00  
  Purchase #2 $94.82   9.798%   $104.1105   $104.11   $104.10   $104.10  
  Purchase #3 $221.89   9.171%   $242.2395   $242.24   $242.25   $242.20  
  Purchase #4 $146.26   3.334%   $151.1363   $151.14   $151.15   $151.10  
  Purchase #5 $195.99   10.423%   $216.418   $216.42   $216.40   $216.40  
  Purchase #6 $194.58   4.576%   $203.484   $203.48   $203.50   $203.50  
  Purchase #7 $122.41   9.721%   $134.3095   $134.31   $134.30   $134.30  
  7 purchase totals = $1,202.82       $1,301.6677   $1,301.67   $1,301.65   $1,301.60