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 $242.35   8.168%   $262.1451   $262.15   $262.15   $262.10  
  Purchase #2 $179.39   7.325%   $192.5303   $192.53   $192.55   $192.50  
  Purchase #3 $19.92   11.311%   $22.1732   $22.17   $22.15   $22.20  
  Purchase #4 $40.89   10.869%   $45.3343   $45.33   $45.35   $45.30  
  Purchase #5 $123.27   8.292%   $133.4915   $133.49   $133.50   $133.50  
  Purchase #6 $141.40   4.783%   $148.1632   $148.16   $148.15   $148.20  
  Purchase #7 $214.39   11.673%   $239.4157   $239.42   $239.40   $239.40  
  7 purchase totals = $961.61       $1,043.2533   $1,043.25   $1,043.25   $1,043.20