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 $67.75   13.355%   $76.798   $76.80   $76.80   $76.80  
  Purchase #2 $216.87   4.254%   $226.0956   $226.10   $226.10   $226.10  
  Purchase #3 $26.99   7.543%   $29.0259   $29.03   $29.05   $29.00  
  Purchase #4 $65.78   10.105%   $72.4271   $72.43   $72.45   $72.40  
  Purchase #5 $86.47   3.567%   $89.5544   $89.55   $89.55   $89.60  
  Purchase #6 $41.98   11.862%   $46.9597   $46.96   $46.95   $47.00  
  Purchase #7 $121.70   11.703%   $135.9426   $135.94   $135.95   $135.90  
  7 purchase totals = $627.54       $676.8033   $676.81   $676.85   $676.80