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 $116.40   8.571%   $126.3766   $126.38   $126.40   $126.40  
  Purchase #2 $232.33   13.391%   $263.4413   $263.44   $263.45   $263.40  
  Purchase #3 $108.35   13.246%   $122.702   $122.70   $122.70   $122.70  
  Purchase #4 $46.46   4.105%   $48.3672   $48.37   $48.35   $48.40  
  Purchase #5 $243.59   7.258%   $261.2698   $261.27   $261.25   $261.30  
  Purchase #6 $44.32   11.629%   $49.474   $49.47   $49.45   $49.50  
  Purchase #7 $168.68   6.126%   $179.0133   $179.01   $179.00   $179.00  
  7 purchase totals = $960.13       $1,050.6442   $1,050.64   $1,050.60   $1,050.70