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 $64.37   13.643%   $73.152   $73.15   $73.15   $73.20  
  Purchase #2 $106.64   7.356%   $114.4844   $114.48   $114.50   $114.50  
  Purchase #3 $178.79   6.611%   $190.6098   $190.61   $190.60   $190.60  
  Purchase #4 $245.46   12.507%   $276.1597   $276.16   $276.15   $276.20  
  Purchase #5 $158.99   4.850%   $166.701   $166.70   $166.70   $166.70  
  Purchase #6 $96.56   3.662%   $100.096   $100.10   $100.10   $100.10  
  Purchase #7 $59.42   12.820%   $67.0376   $67.04   $67.05   $67.00  
  7 purchase totals = $910.23       $988.2405   $988.24   $988.25   $988.30