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 $222.57   10.509%   $245.9599   $245.96   $245.95   $246.00  
  Purchase #2 $143.43   13.657%   $163.0182   $163.02   $163.00   $163.00  
  Purchase #3 $202.63   3.223%   $209.1608   $209.16   $209.15   $209.20  
  Purchase #4 $126.68   5.811%   $134.0414   $134.04   $134.05   $134.00  
  Purchase #5 $105.79   13.738%   $120.3234   $120.32   $120.30   $120.30  
  Purchase #6 $182.62   4.733%   $191.2634   $191.26   $191.25   $191.30  
  Purchase #7 $139.44   3.646%   $144.524   $144.52   $144.50   $144.50  
  7 purchase totals = $1,123.16       $1,208.2911   $1,208.28   $1,208.20   $1,208.30