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 $113.42   12.526%   $127.627   $127.63   $127.65   $127.60  
  Purchase #2 $79.80   6.271%   $84.8043   $84.80   $84.80   $84.80  
  Purchase #3 $162.66   8.604%   $176.6553   $176.66   $176.65   $176.70  
  Purchase #4 $93.83   9.547%   $102.788   $102.79   $102.80   $102.80  
  Purchase #5 $234.92   6.664%   $250.5751   $250.58   $250.60   $250.60  
  Purchase #6 $153.85   6.722%   $164.1918   $164.19   $164.20   $164.20  
  Purchase #7 $167.75   5.692%   $177.2983   $177.30   $177.30   $177.30  
  7 purchase totals = $1,006.23       $1,083.9398   $1,083.95   $1,084.00   $1,084.00