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 $40.86   13.653%   $46.4386   $46.44   $46.45   $46.40  
  Purchase #2 $50.68   4.223%   $52.8202   $52.82   $52.80   $52.80  
  Purchase #3 $146.44   7.628%   $157.6104   $157.61   $157.60   $157.60  
  Purchase #4 $220.60   7.270%   $236.6376   $236.64   $236.65   $236.60  
  Purchase #5 $208.56   3.547%   $215.9576   $215.96   $215.95   $216.00  
  Purchase #6 $118.43   13.564%   $134.4938   $134.49   $134.50   $134.50  
  Purchase #7 $82.42   13.534%   $93.5747   $93.57   $93.55   $93.60  
  7 purchase totals = $867.99       $937.5329   $937.53   $937.50   $937.50