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 $50.60   5.198%   $53.2302   $53.23   $53.25   $53.20  
  Purchase #2 $81.53   4.770%   $85.419   $85.42   $85.40   $85.40  
  Purchase #3 $21.59   13.104%   $24.4192   $24.42   $24.40   $24.40  
  Purchase #4 $236.30   5.110%   $248.3749   $248.37   $248.35   $248.40  
  Purchase #5 $243.56   6.320%   $258.953   $258.95   $258.95   $259.00  
  Purchase #6 $74.84   13.771%   $85.1462   $85.15   $85.15   $85.10  
  Purchase #7 $25.58   3.832%   $26.5602   $26.56   $26.55   $26.60  
  7 purchase totals = $734.00       $782.1027   $782.10   $782.05   $782.10