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 $223.71   13.522%   $253.9601   $253.96   $253.95   $254.00  
  Purchase #2 $180.96   4.566%   $189.2226   $189.22   $189.20   $189.20  
  Purchase #3 $119.77   12.444%   $134.6742   $134.67   $134.65   $134.70  
  Purchase #4 $22.90   11.269%   $25.4806   $25.48   $25.50   $25.50  
  Purchase #5 $236.72   6.719%   $252.6252   $252.63   $252.65   $252.60  
  Purchase #6 $42.83   7.399%   $45.999   $46.00   $46.00   $46.00  
  Purchase #7 $76.31   5.205%   $80.2819   $80.28   $80.30   $80.30  
  7 purchase totals = $903.20       $982.2436   $982.24   $982.25   $982.30