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 $238.63   12.809%   $269.1961   $269.20   $269.20   $269.20  
  Purchase #2 $107.76   7.728%   $116.0877   $116.09   $116.10   $116.10  
  Purchase #3 $216.63   13.225%   $245.2793   $245.28   $245.30   $245.30  
  Purchase #4 $174.97   7.742%   $188.5162   $188.52   $188.50   $188.50  
  Purchase #5 $61.63   3.688%   $63.9029   $63.90   $63.90   $63.90  
  Purchase #6 $197.34   10.762%   $218.5777   $218.58   $218.60   $218.60  
  Purchase #7 $46.81   12.149%   $52.4969   $52.50   $52.50   $52.50  
  7 purchase totals = $1,043.77       $1,154.0568   $1,154.07   $1,154.10   $1,154.10