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 $245.76   5.159%   $258.4388   $258.44   $258.45   $258.40  
  Purchase #2 $38.71   7.496%   $41.6117   $41.61   $41.60   $41.60  
  Purchase #3 $78.49   3.520%   $81.2528   $81.25   $81.25   $81.30  
  Purchase #4 $235.82   12.391%   $265.0405   $265.04   $265.05   $265.00  
  Purchase #5 $107.57   6.743%   $114.8234   $114.82   $114.80   $114.80  
  Purchase #6 $226.78   6.453%   $241.4141   $241.41   $241.40   $241.40  
  Purchase #7 $86.98   4.780%   $91.1376   $91.14   $91.15   $91.10  
  7 purchase totals = $1,020.11       $1,093.7189   $1,093.71   $1,093.70   $1,093.60