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 $61.85   3.356%   $63.9257   $63.93   $63.95   $63.90  
  Purchase #2 $78.81   7.644%   $84.8342   $84.83   $84.85   $84.80  
  Purchase #3 $107.85   7.574%   $116.0186   $116.02   $116.00   $116.00  
  Purchase #4 $92.77   5.719%   $98.0755   $98.08   $98.10   $98.10  
  Purchase #5 $113.40   9.870%   $124.5926   $124.59   $124.60   $124.60  
  Purchase #6 $84.30   13.599%   $95.764   $95.76   $95.75   $95.80  
  Purchase #7 $81.89   8.750%   $89.0554   $89.06   $89.05   $89.10  
  7 purchase totals = $620.87       $672.2660   $672.27   $672.30   $672.30