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 $115.30   9.622%   $126.3942   $126.39   $126.40   $126.40  
  Purchase #2 $174.44   11.128%   $193.8517   $193.85   $193.85   $193.90  
  Purchase #3 $95.90   5.605%   $101.2752   $101.28   $101.30   $101.30  
  Purchase #4 $60.30   10.803%   $66.8142   $66.81   $66.80   $66.80  
  Purchase #5 $130.47   5.737%   $137.9551   $137.96   $137.95   $138.00  
  Purchase #6 $99.97   6.545%   $106.513   $106.51   $106.50   $106.50  
  Purchase #7 $158.39   4.523%   $165.554   $165.55   $165.55   $165.60  
  7 purchase totals = $834.77       $898.3574   $898.35   $898.35   $898.50