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 $162.47   9.114%   $177.2775   $177.28   $177.30   $177.30  
  Purchase #2 $52.89   6.335%   $56.2406   $56.24   $56.25   $56.20  
  Purchase #3 $34.99   3.676%   $36.2762   $36.28   $36.30   $36.30  
  Purchase #4 $153.39   7.329%   $164.632   $164.63   $164.65   $164.60  
  Purchase #5 $154.78   13.847%   $176.2124   $176.21   $176.20   $176.20  
  Purchase #6 $126.28   7.288%   $135.4833   $135.48   $135.50   $135.50  
  Purchase #7 $179.95   13.857%   $204.8857   $204.89   $204.90   $204.90  
  7 purchase totals = $864.75       $951.0077   $951.01   $951.10   $951.00