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 $60.33   7.797%   $65.0339   $65.03   $65.05   $65.00  
  Purchase #2 $198.67   9.671%   $217.8834   $217.88   $217.90   $217.90  
  Purchase #3 $210.92   8.554%   $228.9621   $228.96   $228.95   $229.00  
  Purchase #4 $22.81   5.872%   $24.1494   $24.15   $24.15   $24.10  
  Purchase #5 $5.68   12.715%   $6.4022   $6.40   $6.40   $6.40  
  Purchase #6 $183.31   9.837%   $201.3422   $201.34   $201.35   $201.30  
  Purchase #7 $38.38   10.641%   $42.464   $42.46   $42.45   $42.50  
  7 purchase totals = $720.10       $786.2372   $786.22   $786.25   $786.20