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 $38.75   6.349%   $41.2102   $41.21   $41.20   $41.20  
  Purchase #2 $95.82   9.326%   $104.7562   $104.76   $104.75   $104.80  
  Purchase #3 $163.33   7.699%   $175.9048   $175.90   $175.90   $175.90  
  Purchase #4 $231.85   13.357%   $262.8182   $262.82   $262.80   $262.80  
  Purchase #5 $220.74   10.359%   $243.6065   $243.61   $243.60   $243.60  
  Purchase #6 $25.99   6.177%   $27.5954   $27.60   $27.60   $27.60  
  Purchase #7 $211.34   5.420%   $222.7946   $222.79   $222.80   $222.80  
  7 purchase totals = $987.82       $1,078.6859   $1,078.69   $1,078.65   $1,078.70