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 $164.63   11.105%   $182.9122   $182.91   $182.90   $182.90  
  Purchase #2 $58.75   5.209%   $61.8103   $61.81   $61.80   $61.80  
  Purchase #3 $156.42   5.713%   $165.3563   $165.36   $165.35   $165.40  
  Purchase #4 $118.97   7.535%   $127.9344   $127.93   $127.95   $127.90  
  Purchase #5 $97.40   5.657%   $102.9099   $102.91   $102.90   $102.90  
  Purchase #6 $181.92   8.758%   $197.8526   $197.85   $197.85   $197.90  
  Purchase #7 $117.39   11.240%   $130.5846   $130.58   $130.60   $130.60  
  7 purchase totals = $895.48       $969.3603   $969.35   $969.35   $969.40