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 $226.89   6.767%   $242.2436   $242.24   $242.25   $242.20  
  Purchase #2 $41.83   7.596%   $45.0074   $45.01   $45.00   $45.00  
  Purchase #3 $78.51   4.376%   $81.9456   $81.95   $81.95   $81.90  
  Purchase #4 $155.78   11.318%   $173.4112   $173.41   $173.40   $173.40  
  Purchase #5 $120.68   11.377%   $134.4098   $134.41   $134.40   $134.40  
  Purchase #6 $237.45   10.361%   $262.0522   $262.05   $262.05   $262.10  
  Purchase #7 $127.65   4.673%   $133.6151   $133.62   $133.60   $133.60  
  7 purchase totals = $988.79       $1,072.6849   $1,072.69   $1,072.65   $1,072.60