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 $24.51   5.132%   $25.7679   $25.77   $25.75   $25.80  
  Purchase #2 $222.81   11.265%   $247.9095   $247.91   $247.90   $247.90  
  Purchase #3 $178.94   3.694%   $185.55   $185.55   $185.55   $185.60  
  Purchase #4 $27.99   4.515%   $29.2537   $29.25   $29.25   $29.30  
  Purchase #5 $236.43   5.121%   $248.5376   $248.54   $248.55   $248.50  
  Purchase #6 $105.58   6.758%   $112.7151   $112.72   $112.70   $112.70  
  Purchase #7 $200.28   6.636%   $213.5706   $213.57   $213.55   $213.60  
  7 purchase totals = $996.54       $1,063.3044   $1,063.31   $1,063.25   $1,063.40