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 $33.54   3.450%   $34.6971   $34.70   $34.70   $34.70  
  Purchase #2 $191.71   8.860%   $208.6955   $208.70   $208.70   $208.70  
  Purchase #3 $108.42   4.561%   $113.365   $113.37   $113.35   $113.40  
  Purchase #4 $76.78   10.419%   $84.7797   $84.78   $84.80   $84.80  
  Purchase #5 $239.63   5.261%   $252.2369   $252.24   $252.25   $252.20  
  Purchase #6 $97.50   6.142%   $103.4885   $103.49   $103.50   $103.50  
  Purchase #7 $224.40   13.408%   $254.4876   $254.49   $254.50   $254.50  
  7 purchase totals = $971.98       $1,051.7503   $1,051.77   $1,051.80   $1,051.80