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 $62.34   13.354%   $70.6649   $70.66   $70.65   $70.70  
  Purchase #2 $186.74   3.540%   $193.3506   $193.35   $193.35   $193.40  
  Purchase #3 $93.25   11.778%   $104.233   $104.23   $104.25   $104.20  
  Purchase #4 $139.96   6.164%   $148.5871   $148.59   $148.60   $148.60  
  Purchase #5 $57.91   12.715%   $65.2733   $65.27   $65.25   $65.30  
  Purchase #6 $153.49   11.496%   $171.1352   $171.14   $171.15   $171.10  
  Purchase #7 $119.98   13.691%   $136.4065   $136.41   $136.40   $136.40  
  7 purchase totals = $813.67       $889.6506   $889.65   $889.65   $889.70