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 $58.76   4.197%   $61.2262   $61.23   $61.25   $61.20  
  Purchase #2 $167.79   9.638%   $183.9616   $183.96   $183.95   $184.00  
  Purchase #3 $181.66   5.128%   $190.9755   $190.98   $191.00   $191.00  
  Purchase #4 $172.83   6.675%   $184.3664   $184.37   $184.35   $184.40  
  Purchase #5 $38.55   9.571%   $42.2396   $42.24   $42.25   $42.20  
  Purchase #6 $27.88   10.146%   $30.7087   $30.71   $30.70   $30.70  
  Purchase #7 $18.83   11.754%   $21.0433   $21.04   $21.05   $21.00  
  7 purchase totals = $666.30       $714.5213   $714.53   $714.55   $714.50