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 $69.25   10.193%   $76.3087   $76.31   $76.30   $76.30  
  Purchase #2 $226.42   7.546%   $243.5057   $243.51   $243.50   $243.50  
  Purchase #3 $61.66   8.250%   $66.747   $66.75   $66.75   $66.70  
  Purchase #4 $179.43   6.706%   $191.4626   $191.46   $191.45   $191.50  
  Purchase #5 $28.75   11.608%   $32.0873   $32.09   $32.10   $32.10  
  Purchase #6 $162.76   7.516%   $174.993   $174.99   $175.00   $175.00  
  Purchase #7 $33.43   4.116%   $34.806   $34.81   $34.80   $34.80  
  7 purchase totals = $761.70       $819.9103   $819.92   $819.90   $819.90