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 $123.39   10.706%   $136.6001   $136.60   $136.60   $136.60  
  Purchase #2 $203.81   10.271%   $224.7433   $224.74   $224.75   $224.70  
  Purchase #3 $84.91   13.779%   $96.6097   $96.61   $96.60   $96.60  
  Purchase #4 $218.51   10.579%   $241.6262   $241.63   $241.65   $241.60  
  Purchase #5 $177.26   3.841%   $184.0686   $184.07   $184.05   $184.10  
  Purchase #6 $101.94   12.362%   $114.5418   $114.54   $114.55   $114.50  
  Purchase #7 $148.40   10.389%   $163.8173   $163.82   $163.80   $163.80  
  7 purchase totals = $1,058.22       $1,162.0070   $1,162.01   $1,162.00   $1,161.90