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 $60.29   5.669%   $63.7078   $63.71   $63.70   $63.70  
  Purchase #2 $95.68   9.565%   $104.8318   $104.83   $104.85   $104.80  
  Purchase #3 $210.68   7.452%   $226.3799   $226.38   $226.40   $226.40  
  Purchase #4 $120.44   11.738%   $134.5772   $134.58   $134.60   $134.60  
  Purchase #5 $57.45   13.195%   $65.0305   $65.03   $65.05   $65.00  
  Purchase #6 $64.58   5.859%   $68.3637   $68.36   $68.35   $68.40  
  Purchase #7 $177.72   7.422%   $190.9104   $190.91   $190.90   $190.90  
  7 purchase totals = $786.84       $853.8013   $853.80   $853.85   $853.80