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 $177.55   13.329%   $201.2156   $201.22   $201.20   $201.20  
  Purchase #2 $31.57   11.647%   $35.247   $35.25   $35.25   $35.20  
  Purchase #3 $50.91   5.522%   $53.7213   $53.72   $53.70   $53.70  
  Purchase #4 $77.56   11.598%   $86.5554   $86.56   $86.55   $86.60  
  Purchase #5 $184.70   4.865%   $193.6857   $193.69   $193.70   $193.70  
  Purchase #6 $76.64   4.365%   $79.9853   $79.99   $80.00   $80.00  
  Purchase #7 $145.25   8.872%   $158.1366   $158.14   $158.15   $158.10  
  7 purchase totals = $744.18       $808.5469   $808.57   $808.55   $808.50