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 $35.28   3.548%   $36.5317   $36.53   $36.55   $36.50  
  Purchase #2 $31.91   11.522%   $35.5867   $35.59   $35.60   $35.60  
  Purchase #3 $59.84   4.183%   $62.3431   $62.34   $62.35   $62.30  
  Purchase #4 $48.91   4.491%   $51.1065   $51.11   $51.10   $51.10  
  Purchase #5 $248.92   9.656%   $272.9557   $272.96   $272.95   $273.00  
  Purchase #6 $236.35   12.366%   $265.577   $265.58   $265.60   $265.60  
  Purchase #7 $112.41   5.695%   $118.8117   $118.81   $118.80   $118.80  
  7 purchase totals = $773.62       $842.9124   $842.92   $842.95   $842.90