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 $248.62   5.192%   $261.5284   $261.53   $261.55   $261.50  
  Purchase #2 $41.36   9.782%   $45.4058   $45.41   $45.40   $45.40  
  Purchase #3 $220.37   9.432%   $241.1553   $241.16   $241.15   $241.20  
  Purchase #4 $82.92   5.665%   $87.6174   $87.62   $87.60   $87.60  
  Purchase #5 $42.52   8.355%   $46.0725   $46.07   $46.05   $46.10  
  Purchase #6 $218.97   6.536%   $233.2819   $233.28   $233.30   $233.30  
  Purchase #7 $10.70   8.849%   $11.6468   $11.65   $11.65   $11.60  
  7 purchase totals = $865.46       $926.7081   $926.72   $926.70   $926.70