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 $68.99   5.514%   $72.7941   $72.79   $72.80   $72.80  
  Purchase #2 $222.32   11.354%   $247.5622   $247.56   $247.55   $247.60  
  Purchase #3 $191.34   5.186%   $201.2629   $201.26   $201.25   $201.30  
  Purchase #4 $173.64   8.475%   $188.356   $188.36   $188.35   $188.40  
  Purchase #5 $167.68   10.326%   $184.9946   $184.99   $185.00   $185.00  
  Purchase #6 $69.85   10.102%   $76.9062   $76.91   $76.90   $76.90  
  Purchase #7 $96.68   7.839%   $104.2587   $104.26   $104.25   $104.30  
  7 purchase totals = $990.50       $1,076.1347   $1,076.13   $1,076.10   $1,076.30