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 $56.60   5.202%   $59.5443   $59.54   $59.55   $59.50  
  Purchase #2 $187.82   10.724%   $207.9618   $207.96   $207.95   $208.00  
  Purchase #3 $119.69   12.861%   $135.0833   $135.08   $135.10   $135.10  
  Purchase #4 $209.43   8.225%   $226.6556   $226.66   $226.65   $226.70  
  Purchase #5 $202.66   8.623%   $220.1354   $220.14   $220.15   $220.10  
  Purchase #6 $96.53   8.712%   $104.9397   $104.94   $104.95   $104.90  
  Purchase #7 $23.57   11.823%   $26.3567   $26.36   $26.35   $26.40  
  7 purchase totals = $896.30       $980.6768   $980.68   $980.70   $980.70