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 $216.99   10.425%   $239.6112   $239.61   $239.60   $239.60  
  Purchase #2 $86.43   11.241%   $96.1456   $96.15   $96.15   $96.10  
  Purchase #3 $83.86   7.282%   $89.9667   $89.97   $89.95   $90.00  
  Purchase #4 $179.66   13.214%   $203.4003   $203.40   $203.40   $203.40  
  Purchase #5 $57.38   8.796%   $62.4271   $62.43   $62.45   $62.40  
  Purchase #6 $119.94   12.473%   $134.9001   $134.90   $134.90   $134.90  
  Purchase #7 $152.97   12.231%   $171.6798   $171.68   $171.70   $171.70  
  7 purchase totals = $897.23       $998.1308   $998.14   $998.15   $998.10