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 $239.86   8.810%   $260.9917   $260.99   $261.00   $261.00  
  Purchase #2 $37.93   7.441%   $40.7524   $40.75   $40.75   $40.80  
  Purchase #3 $157.59   6.758%   $168.2399   $168.24   $168.25   $168.20  
  Purchase #4 $112.48   7.249%   $120.6337   $120.63   $120.65   $120.60  
  Purchase #5 $44.94   4.121%   $46.792   $46.79   $46.80   $46.80  
  Purchase #6 $202.77   11.853%   $226.8043   $226.80   $226.80   $226.80  
  Purchase #7 $115.94   4.166%   $120.7701   $120.77   $120.75   $120.80  
  7 purchase totals = $911.51       $984.9841   $984.97   $985.00   $985.00