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 $44.25   5.827%   $46.8284   $46.83   $46.85   $46.80  
  Purchase #2 $231.27   13.526%   $262.5516   $262.55   $262.55   $262.60  
  Purchase #3 $68.36   5.123%   $71.8621   $71.86   $71.85   $71.90  
  Purchase #4 $208.76   13.387%   $236.7067   $236.71   $236.70   $236.70  
  Purchase #5 $83.68   5.154%   $87.9929   $87.99   $88.00   $88.00  
  Purchase #6 $229.73   7.728%   $247.4835   $247.48   $247.50   $247.50  
  Purchase #7 $33.78   11.675%   $37.7238   $37.72   $37.70   $37.70  
  7 purchase totals = $899.83       $991.1490   $991.14   $991.15   $991.20