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 $83.70   3.793%   $86.8747   $86.87   $86.85   $86.90  
  Purchase #2 $234.43   13.856%   $266.9126   $266.91   $266.90   $266.90  
  Purchase #3 $207.76   13.590%   $235.9946   $235.99   $236.00   $236.00  
  Purchase #4 $46.54   10.321%   $51.3434   $51.34   $51.35   $51.30  
  Purchase #5 $120.96   4.515%   $126.4213   $126.42   $126.40   $126.40  
  Purchase #6 $235.46   5.442%   $248.2737   $248.27   $248.25   $248.30  
  Purchase #7 $15.87   9.691%   $17.408   $17.41   $17.40   $17.40  
  7 purchase totals = $944.72       $1,033.2283   $1,033.21   $1,033.15   $1,033.20