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 $33.62   6.556%   $35.8241   $35.82   $35.80   $35.80  
  Purchase #2 $231.57   13.537%   $262.9176   $262.92   $262.90   $262.90  
  Purchase #3 $198.83   6.179%   $211.1157   $211.12   $211.10   $211.10  
  Purchase #4 $44.92   4.430%   $46.91   $46.91   $46.90   $46.90  
  Purchase #5 $183.43   10.144%   $202.0371   $202.04   $202.05   $202.00  
  Purchase #6 $163.94   5.441%   $172.86   $172.86   $172.85   $172.90  
  Purchase #7 $122.85   10.818%   $136.1399   $136.14   $136.15   $136.10  
  7 purchase totals = $979.16       $1,067.8044   $1,067.81   $1,067.75   $1,067.70