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 $71.61   8.620%   $77.7828   $77.78   $77.80   $77.80  
  Purchase #2 $168.89   10.165%   $186.0577   $186.06   $186.05   $186.10  
  Purchase #3 $102.71   11.481%   $114.5021   $114.50   $114.50   $114.50  
  Purchase #4 $167.30   4.848%   $175.4107   $175.41   $175.40   $175.40  
  Purchase #5 $177.89   13.537%   $201.971   $201.97   $201.95   $202.00  
  Purchase #6 $185.76   6.154%   $197.1917   $197.19   $197.20   $197.20  
  Purchase #7 $196.95   6.861%   $210.4627   $210.46   $210.45   $210.50  
  7 purchase totals = $1,071.11       $1,163.3787   $1,163.37   $1,163.35   $1,163.50