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 $241.77   9.869%   $265.6303   $265.63   $265.65   $265.60  
  Purchase #2 $155.51   13.795%   $176.9626   $176.96   $176.95   $177.00  
  Purchase #3 $19.90   3.864%   $20.6689   $20.67   $20.65   $20.70  
  Purchase #4 $195.69   5.491%   $206.4353   $206.44   $206.45   $206.40  
  Purchase #5 $209.91   12.622%   $236.4048   $236.40   $236.40   $236.40  
  Purchase #6 $104.39   7.454%   $112.1712   $112.17   $112.15   $112.20  
  Purchase #7 $55.47   3.465%   $57.392   $57.39   $57.40   $57.40  
  7 purchase totals = $982.64       $1,075.6651   $1,075.66   $1,075.65   $1,075.70