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 $162.91   13.299%   $184.5754   $184.58   $184.60   $184.60  
  Purchase #2 $50.53   12.613%   $56.9033   $56.90   $56.90   $56.90  
  Purchase #3 $185.37   4.585%   $193.8692   $193.87   $193.85   $193.90  
  Purchase #4 $164.85   12.646%   $185.6969   $185.70   $185.70   $185.70  
  Purchase #5 $50.77   10.306%   $56.0024   $56.00   $56.00   $56.00  
  Purchase #6 $116.42   12.332%   $130.7769   $130.78   $130.80   $130.80  
  Purchase #7 $173.55   8.380%   $188.0935   $188.09   $188.10   $188.10  
  7 purchase totals = $904.40       $995.9176   $995.92   $995.95   $996.00