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 $96.29   11.629%   $107.4876   $107.49   $107.50   $107.50  
  Purchase #2 $135.51   9.149%   $147.9078   $147.91   $147.90   $147.90  
  Purchase #3 $187.77   3.104%   $193.5984   $193.60   $193.60   $193.60  
  Purchase #4 $131.49   13.835%   $149.6816   $149.68   $149.70   $149.70  
  Purchase #5 $185.34   5.506%   $195.5448   $195.54   $195.55   $195.50  
  Purchase #6 $8.58   12.267%   $9.6325   $9.63   $9.65   $9.60  
  Purchase #7 $236.76   11.335%   $263.5967   $263.60   $263.60   $263.60  
  7 purchase totals = $981.74       $1,067.4494   $1,067.45   $1,067.50   $1,067.40