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 $159.32   10.639%   $176.2701   $176.27   $176.25   $176.30  
  Purchase #2 $138.51   10.738%   $153.3832   $153.38   $153.40   $153.40  
  Purchase #3 $68.81   12.459%   $77.383   $77.38   $77.40   $77.40  
  Purchase #4 $31.75   9.542%   $34.7796   $34.78   $34.80   $34.80  
  Purchase #5 $15.88   5.863%   $16.811   $16.81   $16.80   $16.80  
  Purchase #6 $249.26   8.120%   $269.4999   $269.50   $269.50   $269.50  
  Purchase #7 $36.47   5.196%   $38.365   $38.37   $38.35   $38.40  
  7 purchase totals = $700.00       $766.4918   $766.49   $766.50   $766.60