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 $214.56   13.833%   $244.2401   $244.24   $244.25   $244.20  
  Purchase #2 $123.59   8.634%   $134.2608   $134.26   $134.25   $134.30  
  Purchase #3 $224.81   6.111%   $238.5481   $238.55   $238.55   $238.50  
  Purchase #4 $129.76   5.822%   $137.3146   $137.31   $137.30   $137.30  
  Purchase #5 $167.45   5.445%   $176.5677   $176.57   $176.55   $176.60  
  Purchase #6 $41.36   7.319%   $44.3871   $44.39   $44.40   $44.40  
  Purchase #7 $6.70   8.863%   $7.2938   $7.29   $7.30   $7.30  
  7 purchase totals = $908.23       $982.6122   $982.61   $982.60   $982.60