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 $160.69   9.632%   $176.1677   $176.17   $176.15   $176.20  
  Purchase #2 $58.89   13.318%   $66.733   $66.73   $66.75   $66.70  
  Purchase #3 $61.90   6.313%   $65.8077   $65.81   $65.80   $65.80  
  Purchase #4 $226.36   6.639%   $241.388   $241.39   $241.40   $241.40  
  Purchase #5 $58.72   7.404%   $63.0676   $63.07   $63.05   $63.10  
  Purchase #6 $60.80   11.520%   $67.8042   $67.80   $67.80   $67.80  
  Purchase #7 $23.35   13.450%   $26.4906   $26.49   $26.50   $26.50  
  7 purchase totals = $650.71       $707.4588   $707.46   $707.45   $707.50