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 $147.42   6.512%   $157.02   $157.02   $157.00   $157.00  
  Purchase #2 $51.28   9.657%   $56.2321   $56.23   $56.25   $56.20  
  Purchase #3 $106.73   6.816%   $114.0047   $114.00   $114.00   $114.00  
  Purchase #4 $214.50   11.858%   $239.9354   $239.94   $239.95   $239.90  
  Purchase #5 $168.73   9.773%   $185.22   $185.22   $185.20   $185.20  
  Purchase #6 $238.55   4.382%   $249.0033   $249.00   $249.00   $249.00  
  Purchase #7 $18.31   6.739%   $19.5439   $19.54   $19.55   $19.50  
  7 purchase totals = $945.52       $1,020.9594   $1,020.95   $1,020.95   $1,020.80