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 $183.93   6.615%   $196.097   $196.10   $196.10   $196.10  
  Purchase #2 $34.63   5.431%   $36.5108   $36.51   $36.50   $36.50  
  Purchase #3 $32.49   6.798%   $34.6987   $34.70   $34.70   $34.70  
  Purchase #4 $115.29   11.869%   $128.9738   $128.97   $128.95   $129.00  
  Purchase #5 $198.30   11.587%   $221.277   $221.28   $221.30   $221.30  
  Purchase #6 $98.28   4.406%   $102.6102   $102.61   $102.60   $102.60  
  Purchase #7 $53.42   6.594%   $56.9425   $56.94   $56.95   $56.90  
  7 purchase totals = $716.34       $777.1100   $777.11   $777.10   $777.10