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 $67.66   13.666%   $76.9064   $76.91   $76.90   $76.90  
  Purchase #2 $183.99   13.519%   $208.8636   $208.86   $208.85   $208.90  
  Purchase #3 $115.61   7.691%   $124.5016   $124.50   $124.50   $124.50  
  Purchase #4 $35.87   13.598%   $40.7476   $40.75   $40.75   $40.70  
  Purchase #5 $33.57   6.654%   $35.8037   $35.80   $35.80   $35.80  
  Purchase #6 $28.30   4.287%   $29.5132   $29.51   $29.50   $29.50  
  Purchase #7 $206.94   8.595%   $224.7265   $224.73   $224.75   $224.70  
  7 purchase totals = $671.94       $741.0626   $741.06   $741.05   $741.00