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 $241.67   6.747%   $257.9755   $257.98   $258.00   $258.00  
  Purchase #2 $185.47   3.660%   $192.2582   $192.26   $192.25   $192.30  
  Purchase #3 $27.28   11.624%   $30.451   $30.45   $30.45   $30.50  
  Purchase #4 $205.26   4.179%   $213.8378   $213.84   $213.85   $213.80  
  Purchase #5 $42.80   6.545%   $45.6013   $45.60   $45.60   $45.60  
  Purchase #6 $103.91   5.574%   $109.7019   $109.70   $109.70   $109.70  
  Purchase #7 $250.54   5.561%   $264.4725   $264.47   $264.45   $264.50  
  7 purchase totals = $1,056.93       $1,114.2982   $1,114.30   $1,114.30   $1,114.40