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 $119.66   5.661%   $126.434   $126.43   $126.45   $126.40  
  Purchase #2 $244.72   3.149%   $252.4262   $252.43   $252.45   $252.40  
  Purchase #3 $120.41   9.575%   $131.9393   $131.94   $131.95   $131.90  
  Purchase #4 $226.62   9.271%   $247.6299   $247.63   $247.65   $247.60  
  Purchase #5 $188.48   3.294%   $194.6885   $194.69   $194.70   $194.70  
  Purchase #6 $184.28   6.587%   $196.4185   $196.42   $196.40   $196.40  
  Purchase #7 $160.38   3.462%   $165.9324   $165.93   $165.95   $165.90  
  7 purchase totals = $1,244.55       $1,315.4688   $1,315.47   $1,315.55   $1,315.30