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 $63.64   10.628%   $70.4037   $70.40   $70.40   $70.40  
  Purchase #2 $216.86   9.244%   $236.9065   $236.91   $236.90   $236.90  
  Purchase #3 $66.43   3.816%   $68.965   $68.97   $68.95   $69.00  
  Purchase #4 $171.53   7.464%   $184.333   $184.33   $184.35   $184.30  
  Purchase #5 $37.33   12.337%   $41.9354   $41.94   $41.95   $41.90  
  Purchase #6 $97.51   10.425%   $107.6754   $107.68   $107.70   $107.70  
  Purchase #7 $248.41   11.442%   $276.8331   $276.83   $276.85   $276.80  
  7 purchase totals = $901.71       $987.0521   $987.06   $987.10   $987.00