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 $34.52   5.139%   $36.294   $36.29   $36.30   $36.30  
  Purchase #2 $228.86   9.327%   $250.2058   $250.21   $250.20   $250.20  
  Purchase #3 $129.25   7.475%   $138.9114   $138.91   $138.90   $138.90  
  Purchase #4 $110.57   4.276%   $115.298   $115.30   $115.30   $115.30  
  Purchase #5 $23.53   3.655%   $24.39   $24.39   $24.40   $24.40  
  Purchase #6 $248.34   5.307%   $261.5194   $261.52   $261.50   $261.50  
  Purchase #7 $116.28   8.386%   $126.0312   $126.03   $126.05   $126.00  
  7 purchase totals = $891.35       $952.6498   $952.65   $952.65   $952.60