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 $245.50   9.773%   $269.4927   $269.49   $269.50   $269.50  
  Purchase #2 $218.89   7.564%   $235.4468   $235.45   $235.45   $235.40  
  Purchase #3 $65.76   7.728%   $70.8419   $70.84   $70.85   $70.80  
  Purchase #4 $178.98   4.739%   $187.4619   $187.46   $187.45   $187.50  
  Purchase #5 $191.57   8.577%   $208.001   $208.00   $208.00   $208.00  
  Purchase #6 $236.43   9.429%   $258.723   $258.72   $258.70   $258.70  
  Purchase #7 $34.46   13.417%   $39.0835   $39.08   $39.10   $39.10  
  7 purchase totals = $1,171.59       $1,269.0508   $1,269.04   $1,269.05   $1,269.00