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 $23.87   8.665%   $25.9383   $25.94   $25.95   $25.90  
  Purchase #2 $234.99   11.622%   $262.3005   $262.30   $262.30   $262.30  
  Purchase #3 $58.37   7.111%   $62.5207   $62.52   $62.50   $62.50  
  Purchase #4 $10.88   8.293%   $11.7823   $11.78   $11.80   $11.80  
  Purchase #5 $230.98   7.429%   $248.1395   $248.14   $248.15   $248.10  
  Purchase #6 $180.49   9.262%   $197.207   $197.21   $197.20   $197.20  
  Purchase #7 $168.72   10.271%   $186.0492   $186.05   $186.05   $186.00  
  7 purchase totals = $908.30       $993.9375   $993.94   $993.95   $993.80