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 $141.78   8.790%   $154.2425   $154.24   $154.25   $154.20  
  Purchase #2 $233.90   6.424%   $248.9257   $248.93   $248.95   $248.90  
  Purchase #3 $136.45   7.238%   $146.3263   $146.33   $146.35   $146.30  
  Purchase #4 $217.58   4.388%   $227.1274   $227.13   $227.15   $227.10  
  Purchase #5 $115.50   8.274%   $125.0565   $125.06   $125.05   $125.10  
  Purchase #6 $225.71   4.357%   $235.5442   $235.54   $235.55   $235.50  
  Purchase #7 $51.71   8.749%   $56.2341   $56.23   $56.25   $56.20  
  7 purchase totals = $1,122.63       $1,193.4567   $1,193.46   $1,193.55   $1,193.30