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 $60.77   8.433%   $65.8947   $65.89   $65.90   $65.90  
  Purchase #2 $239.55   13.757%   $272.5049   $272.50   $272.50   $272.50  
  Purchase #3 $231.52   4.195%   $241.2323   $241.23   $241.25   $241.20  
  Purchase #4 $126.49   4.859%   $132.6361   $132.64   $132.65   $132.60  
  Purchase #5 $46.58   3.583%   $48.249   $48.25   $48.25   $48.20  
  Purchase #6 $72.49   5.647%   $76.5835   $76.58   $76.60   $76.60  
  Purchase #7 $196.84   11.343%   $219.1676   $219.17   $219.15   $219.20  
  7 purchase totals = $974.24       $1,056.2681   $1,056.26   $1,056.30   $1,056.20