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 $56.71   4.305%   $59.1514   $59.15   $59.15   $59.20  
  Purchase #2 $177.61   6.209%   $188.6378   $188.64   $188.65   $188.60  
  Purchase #3 $215.36   12.622%   $242.5427   $242.54   $242.55   $242.50  
  Purchase #4 $113.95   12.187%   $127.8371   $127.84   $127.85   $127.80  
  Purchase #5 $223.41   5.821%   $236.4147   $236.41   $236.40   $236.40  
  Purchase #6 $135.87   8.487%   $147.4013   $147.40   $147.40   $147.40  
  Purchase #7 $5.43   12.380%   $6.1022   $6.10   $6.10   $6.10  
  7 purchase totals = $928.34       $1,008.0872   $1,008.08   $1,008.10   $1,008.00