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 $250.30   6.569%   $266.7422   $266.74   $266.75   $266.70  
  Purchase #2 $222.45   5.859%   $235.4833   $235.48   $235.50   $235.50  
  Purchase #3 $14.54   10.660%   $16.09   $16.09   $16.10   $16.10  
  Purchase #4 $67.33   5.633%   $71.1227   $71.12   $71.10   $71.10  
  Purchase #5 $104.67   13.829%   $119.1448   $119.14   $119.15   $119.10  
  Purchase #6 $158.49   10.659%   $175.3834   $175.38   $175.40   $175.40  
  Purchase #7 $163.44   10.632%   $180.8169   $180.82   $180.80   $180.80  
  7 purchase totals = $981.22       $1,064.7833   $1,064.77   $1,064.80   $1,064.70