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 $115.52   5.371%   $121.7246   $121.72   $121.70   $121.70  
  Purchase #2 $237.48   10.298%   $261.9357   $261.94   $261.95   $261.90  
  Purchase #3 $34.74   4.410%   $36.272   $36.27   $36.25   $36.30  
  Purchase #4 $184.39   3.371%   $190.6058   $190.61   $190.60   $190.60  
  Purchase #5 $86.43   8.519%   $93.793   $93.79   $93.80   $93.80  
  Purchase #6 $161.53   10.135%   $177.9011   $177.90   $177.90   $177.90  
  Purchase #7 $50.76   6.851%   $54.2376   $54.24   $54.25   $54.20  
  7 purchase totals = $870.85       $936.4698   $936.47   $936.45   $936.40