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 $79.77   7.868%   $86.0463   $86.05   $86.05   $86.00  
  Purchase #2 $114.47   4.487%   $119.6063   $119.61   $119.60   $119.60  
  Purchase #3 $197.30   4.701%   $206.5751   $206.58   $206.60   $206.60  
  Purchase #4 $96.72   11.754%   $108.0885   $108.09   $108.10   $108.10  
  Purchase #5 $130.60   13.738%   $148.5418   $148.54   $148.55   $148.50  
  Purchase #6 $203.96   10.723%   $225.8306   $225.83   $225.85   $225.80  
  Purchase #7 $21.87   12.861%   $24.6827   $24.68   $24.70   $24.70  
  7 purchase totals = $844.69       $919.3713   $919.38   $919.45   $919.30