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 $243.96   10.358%   $269.2294   $269.23   $269.25   $269.20  
  Purchase #2 $122.42   11.242%   $136.1825   $136.18   $136.20   $136.20  
  Purchase #3 $219.68   3.302%   $226.9338   $226.93   $226.95   $226.90  
  Purchase #4 $250.59   12.816%   $282.7056   $282.71   $282.70   $282.70  
  Purchase #5 $196.54   12.742%   $221.5831   $221.58   $221.60   $221.60  
  Purchase #6 $204.40   8.863%   $222.516   $222.52   $222.50   $222.50  
  Purchase #7 $58.34   7.572%   $62.7575   $62.76   $62.75   $62.80  
  7 purchase totals = $1,295.93       $1,421.9079   $1,421.91   $1,421.95   $1,421.90