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 $161.95   3.271%   $167.2474   $167.25   $167.25   $167.20  
  Purchase #2 $196.43   11.854%   $219.7148   $219.71   $219.70   $219.70  
  Purchase #3 $48.88   12.107%   $54.7979   $54.80   $54.80   $54.80  
  Purchase #4 $41.69   12.308%   $46.8212   $46.82   $46.80   $46.80  
  Purchase #5 $225.83   11.781%   $252.435   $252.44   $252.45   $252.40  
  Purchase #6 $40.99   3.204%   $42.3033   $42.30   $42.30   $42.30  
  Purchase #7 $242.28   7.742%   $261.0373   $261.04   $261.05   $261.00  
  7 purchase totals = $958.05       $1,044.3569   $1,044.36   $1,044.35   $1,044.20