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 $156.85   8.728%   $170.5399   $170.54   $170.55   $170.50  
  Purchase #2 $224.88   4.352%   $234.6668   $234.67   $234.65   $234.70  
  Purchase #3 $245.64   5.205%   $258.4256   $258.43   $258.45   $258.40  
  Purchase #4 $119.34   6.844%   $127.5076   $127.51   $127.50   $127.50  
  Purchase #5 $185.32   9.659%   $203.2201   $203.22   $203.20   $203.20  
  Purchase #6 $228.61   10.605%   $252.8541   $252.85   $252.85   $252.90  
  Purchase #7 $168.92   3.758%   $175.268   $175.27   $175.25   $175.30  
  7 purchase totals = $1,329.56       $1,422.4821   $1,422.49   $1,422.45   $1,422.50