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 $81.39   5.283%   $85.6898   $85.69   $85.70   $85.70  
  Purchase #2 $23.41   10.358%   $25.8348   $25.83   $25.85   $25.80  
  Purchase #3 $120.30   6.159%   $127.7093   $127.71   $127.70   $127.70  
  Purchase #4 $249.89   11.209%   $277.9002   $277.90   $277.90   $277.90  
  Purchase #5 $96.50   3.807%   $100.1738   $100.17   $100.15   $100.20  
  Purchase #6 $162.36   5.646%   $171.5268   $171.53   $171.55   $171.50  
  Purchase #7 $238.28   5.823%   $252.155   $252.16   $252.15   $252.20  
  7 purchase totals = $972.13       $1,040.9897   $1,040.99   $1,041.00   $1,041.00