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 $154.95   7.741%   $166.9447   $166.94   $166.95   $166.90  
  Purchase #2 $227.65   10.807%   $252.2521   $252.25   $252.25   $252.30  
  Purchase #3 $60.34   8.491%   $65.4635   $65.46   $65.45   $65.50  
  Purchase #4 $166.36   9.131%   $181.5503   $181.55   $181.55   $181.60  
  Purchase #5 $12.77   8.850%   $13.9001   $13.90   $13.90   $13.90  
  Purchase #6 $127.48   5.269%   $134.1969   $134.20   $134.20   $134.20  
  Purchase #7 $214.67   7.770%   $231.3499   $231.35   $231.35   $231.30  
  7 purchase totals = $964.22       $1,045.6575   $1,045.65   $1,045.65   $1,045.70