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 $82.47   3.808%   $85.6105   $85.61   $85.60   $85.60  
  Purchase #2 $218.25   11.662%   $243.7023   $243.70   $243.70   $243.70  
  Purchase #3 $154.60   11.823%   $172.8784   $172.88   $172.90   $172.90  
  Purchase #4 $107.96   4.632%   $112.9607   $112.96   $112.95   $113.00  
  Purchase #5 $221.72   8.738%   $241.0939   $241.09   $241.10   $241.10  
  Purchase #6 $237.74   8.747%   $258.5351   $258.54   $258.55   $258.50  
  Purchase #7 $5.97   6.546%   $6.3608   $6.36   $6.35   $6.40  
  7 purchase totals = $1,028.71       $1,121.1417   $1,121.14   $1,121.15   $1,121.20