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 $238.58   12.782%   $269.0753   $269.08   $269.10   $269.10  
  Purchase #2 $169.37   12.287%   $190.1805   $190.18   $190.20   $190.20  
  Purchase #3 $73.99   12.302%   $83.0922   $83.09   $83.10   $83.10  
  Purchase #4 $98.55   7.189%   $105.6348   $105.63   $105.65   $105.60  
  Purchase #5 $107.76   6.718%   $114.9993   $115.00   $115.00   $115.00  
  Purchase #6 $222.83   5.696%   $235.5224   $235.52   $235.50   $235.50  
  Purchase #7 $97.73   8.391%   $105.9305   $105.93   $105.95   $105.90  
  7 purchase totals = $1,008.81       $1,104.4350   $1,104.43   $1,104.50   $1,104.40