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 $230.94   5.355%   $243.3068   $243.31   $243.30   $243.30  
  Purchase #2 $25.83   8.252%   $27.9615   $27.96   $27.95   $28.00  
  Purchase #3 $131.61   12.179%   $147.6388   $147.64   $147.65   $147.60  
  Purchase #4 $109.27   4.563%   $114.256   $114.26   $114.25   $114.30  
  Purchase #5 $60.82   8.614%   $66.059   $66.06   $66.05   $66.10  
  Purchase #6 $237.55   4.493%   $248.2231   $248.22   $248.20   $248.20  
  Purchase #7 $190.72   8.486%   $206.9045   $206.90   $206.90   $206.90  
  7 purchase totals = $986.74       $1,054.3497   $1,054.35   $1,054.30   $1,054.40