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 $72.97   4.536%   $76.2799   $76.28   $76.30   $76.30  
  Purchase #2 $217.97   13.800%   $248.0499   $248.05   $248.05   $248.00  
  Purchase #3 $79.88   12.133%   $89.5718   $89.57   $89.55   $89.60  
  Purchase #4 $67.45   5.241%   $70.9851   $70.99   $71.00   $71.00  
  Purchase #5 $93.86   10.468%   $103.6853   $103.69   $103.70   $103.70  
  Purchase #6 $146.81   12.859%   $165.6883   $165.69   $165.70   $165.70  
  Purchase #7 $224.96   9.224%   $245.7103   $245.71   $245.70   $245.70  
  7 purchase totals = $903.90       $999.9706   $999.98   $1,000.00   $1,000.00