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 $65.82   6.259%   $69.9397   $69.94   $69.95   $69.90  
  Purchase #2 $228.81   10.557%   $252.9655   $252.97   $252.95   $253.00  
  Purchase #3 $209.26   5.551%   $220.876   $220.88   $220.90   $220.90  
  Purchase #4 $192.27   11.658%   $214.6848   $214.68   $214.70   $214.70  
  Purchase #5 $81.37   4.713%   $85.205   $85.21   $85.20   $85.20  
  Purchase #6 $82.73   7.486%   $88.9232   $88.92   $88.90   $88.90  
  Purchase #7 $237.27   8.503%   $257.4451   $257.45   $257.45   $257.40  
  7 purchase totals = $1,097.53       $1,190.0393   $1,190.05   $1,190.05   $1,190.00