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 $241.97   3.328%   $250.0228   $250.02   $250.00   $250.00  
  Purchase #2 $117.28   6.801%   $125.2562   $125.26   $125.25   $125.30  
  Purchase #3 $118.71   5.690%   $125.4646   $125.46   $125.45   $125.50  
  Purchase #4 $166.89   8.615%   $181.2676   $181.27   $181.25   $181.30  
  Purchase #5 $209.27   7.485%   $224.9339   $224.93   $224.95   $224.90  
  Purchase #6 $37.48   8.330%   $40.6021   $40.60   $40.60   $40.60  
  Purchase #7 $163.64   13.292%   $185.391   $185.39   $185.40   $185.40  
  7 purchase totals = $1,055.24       $1,132.9382   $1,132.93   $1,132.90   $1,133.00