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 $124.32   13.119%   $140.6295   $140.63   $140.65   $140.60  
  Purchase #2 $196.38   10.823%   $217.6342   $217.63   $217.65   $217.60  
  Purchase #3 $23.26   12.760%   $26.228   $26.23   $26.25   $26.20  
  Purchase #4 $55.87   9.536%   $61.1978   $61.20   $61.20   $61.20  
  Purchase #5 $65.93   6.790%   $70.4066   $70.41   $70.40   $70.40  
  Purchase #6 $116.96   11.242%   $130.1086   $130.11   $130.10   $130.10  
  Purchase #7 $113.26   3.106%   $116.7779   $116.78   $116.80   $116.80  
  7 purchase totals = $695.98       $762.9826   $762.99   $763.05   $762.90