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 $152.92   8.112%   $165.3249   $165.32   $165.30   $165.30  
  Purchase #2 $62.33   10.563%   $68.9139   $68.91   $68.90   $68.90  
  Purchase #3 $182.67   4.805%   $191.4473   $191.45   $191.45   $191.40  
  Purchase #4 $248.76   6.690%   $265.402   $265.40   $265.40   $265.40  
  Purchase #5 $55.95   11.786%   $62.5443   $62.54   $62.55   $62.50  
  Purchase #6 $101.40   13.665%   $115.2563   $115.26   $115.25   $115.30  
  Purchase #7 $161.40   10.748%   $178.7473   $178.75   $178.75   $178.70  
  7 purchase totals = $965.43       $1,047.6360   $1,047.63   $1,047.60   $1,047.50