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 $245.38   6.764%   $261.9775   $261.98   $262.00   $262.00  
  Purchase #2 $234.69   10.815%   $260.0717   $260.07   $260.05   $260.10  
  Purchase #3 $191.36   8.315%   $207.2716   $207.27   $207.25   $207.30  
  Purchase #4 $68.41   6.258%   $72.6911   $72.69   $72.70   $72.70  
  Purchase #5 $121.39   5.315%   $127.8419   $127.84   $127.85   $127.80  
  Purchase #6 $123.80   12.522%   $139.3022   $139.30   $139.30   $139.30  
  Purchase #7 $69.98   10.500%   $77.3279   $77.33   $77.35   $77.30  
  7 purchase totals = $1,055.01       $1,146.4839   $1,146.48   $1,146.50   $1,146.50