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 $243.91   10.201%   $268.7913   $268.79   $268.80   $268.80  
  Purchase #2 $157.89   4.784%   $165.4435   $165.44   $165.45   $165.40  
  Purchase #3 $34.39   3.322%   $35.5324   $35.53   $35.55   $35.50  
  Purchase #4 $194.25   9.524%   $212.7504   $212.75   $212.75   $212.80  
  Purchase #5 $53.99   7.131%   $57.84   $57.84   $57.85   $57.80  
  Purchase #6 $177.40   11.728%   $198.2055   $198.21   $198.20   $198.20  
  Purchase #7 $37.34   3.188%   $38.5304   $38.53   $38.55   $38.50  
  7 purchase totals = $899.17       $977.0935   $977.09   $977.15   $977.00