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 $240.57   11.654%   $268.606   $268.61   $268.60   $268.60  
  Purchase #2 $177.89   5.477%   $187.633   $187.63   $187.65   $187.60  
  Purchase #3 $23.30   5.519%   $24.5859   $24.59   $24.60   $24.60  
  Purchase #4 $228.25   8.653%   $248.0005   $248.00   $248.00   $248.00  
  Purchase #5 $245.70   9.519%   $269.0882   $269.09   $269.10   $269.10  
  Purchase #6 $114.61   12.793%   $129.2721   $129.27   $129.25   $129.30  
  Purchase #7 $110.88   8.673%   $120.4966   $120.50   $120.50   $120.50  
  7 purchase totals = $1,141.20       $1,247.6823   $1,247.69   $1,247.70   $1,247.70