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 $248.93   3.860%   $258.5387   $258.54   $258.55   $258.50  
  Purchase #2 $235.35   12.596%   $264.9947   $264.99   $265.00   $265.00  
  Purchase #3 $192.83   5.538%   $203.5089   $203.51   $203.50   $203.50  
  Purchase #4 $211.31   7.675%   $227.528   $227.53   $227.55   $227.50  
  Purchase #5 $44.50   4.302%   $46.4144   $46.41   $46.40   $46.40  
  Purchase #6 $166.58   6.410%   $177.2578   $177.26   $177.25   $177.30  
  Purchase #7 $56.35   11.874%   $63.041   $63.04   $63.05   $63.00  
  7 purchase totals = $1,155.85       $1,241.2835   $1,241.28   $1,241.30   $1,241.20