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 $62.54   4.444%   $65.3193   $65.32   $65.30   $65.30  
  Purchase #2 $100.83   3.697%   $104.5577   $104.56   $104.55   $104.60  
  Purchase #3 $141.75   9.832%   $155.6869   $155.69   $155.70   $155.70  
  Purchase #4 $55.61   4.159%   $57.9228   $57.92   $57.90   $57.90  
  Purchase #5 $165.31   11.104%   $183.666   $183.67   $183.65   $183.70  
  Purchase #6 $118.95   8.197%   $128.7003   $128.70   $128.70   $128.70  
  Purchase #7 $242.63   8.543%   $263.3579   $263.36   $263.35   $263.40  
  7 purchase totals = $887.62       $959.2109   $959.22   $959.15   $959.30