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 $214.90   13.348%   $243.5849   $243.58   $243.60   $243.60  
  Purchase #2 $162.82   3.638%   $168.7434   $168.74   $168.75   $168.70  
  Purchase #3 $155.31   5.665%   $164.1083   $164.11   $164.10   $164.10  
  Purchase #4 $239.61   5.413%   $252.5801   $252.58   $252.60   $252.60  
  Purchase #5 $174.64   13.412%   $198.0627   $198.06   $198.05   $198.10  
  Purchase #6 $94.91   10.844%   $105.202   $105.20   $105.20   $105.20  
  Purchase #7 $60.72   8.623%   $65.9559   $65.96   $65.95   $66.00  
  7 purchase totals = $1,102.91       $1,198.2373   $1,198.23   $1,198.25   $1,198.30