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 $114.98   8.434%   $124.6774   $124.68   $124.70   $124.70  
  Purchase #2 $94.51   7.521%   $101.6181   $101.62   $101.60   $101.60  
  Purchase #3 $119.58   6.149%   $126.933   $126.93   $126.95   $126.90  
  Purchase #4 $241.82   10.287%   $266.696   $266.70   $266.70   $266.70  
  Purchase #5 $220.71   5.671%   $233.2265   $233.23   $233.25   $233.20  
  Purchase #6 $232.97   12.745%   $262.662   $262.66   $262.65   $262.70  
  Purchase #7 $152.42   11.839%   $170.465   $170.47   $170.45   $170.50  
  7 purchase totals = $1,176.99       $1,286.2780   $1,286.29   $1,286.30   $1,286.30