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 $15.57   9.546%   $17.0563   $17.06   $17.05   $17.10  
  Purchase #2 $159.83   6.168%   $169.6883   $169.69   $169.70   $169.70  
  Purchase #3 $209.96   12.109%   $235.3841   $235.38   $235.40   $235.40  
  Purchase #4 $240.44   3.269%   $248.3   $248.30   $248.30   $248.30  
  Purchase #5 $149.47   5.874%   $158.2499   $158.25   $158.25   $158.20  
  Purchase #6 $5.43   10.718%   $6.012   $6.01   $6.00   $6.00  
  Purchase #7 $53.83   13.815%   $61.2666   $61.27   $61.25   $61.30  
  7 purchase totals = $834.53       $895.9572   $895.96   $895.95   $896.00