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 $191.79   11.120%   $213.117   $213.12   $213.10   $213.10  
  Purchase #2 $123.69   7.811%   $133.3514   $133.35   $133.35   $133.40  
  Purchase #3 $177.32   4.387%   $185.099   $185.10   $185.10   $185.10  
  Purchase #4 $163.36   11.553%   $182.233   $182.23   $182.25   $182.20  
  Purchase #5 $248.66   3.132%   $256.448   $256.45   $256.45   $256.40  
  Purchase #6 $23.43   4.324%   $24.4431   $24.44   $24.45   $24.40  
  Purchase #7 $234.69   6.796%   $250.6395   $250.64   $250.65   $250.60  
  7 purchase totals = $1,162.94       $1,245.3310   $1,245.33   $1,245.35   $1,245.20