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 $58.86   8.158%   $63.6618   $63.66   $63.65   $63.70  
  Purchase #2 $25.80   11.389%   $28.7384   $28.74   $28.75   $28.70  
  Purchase #3 $107.45   10.522%   $118.7559   $118.76   $118.75   $118.80  
  Purchase #4 $185.47   4.406%   $193.6418   $193.64   $193.65   $193.60  
  Purchase #5 $47.61   13.590%   $54.0802   $54.08   $54.10   $54.10  
  Purchase #6 $147.31   9.611%   $161.468   $161.47   $161.45   $161.50  
  Purchase #7 $239.33   11.521%   $266.9032   $266.90   $266.90   $266.90  
  7 purchase totals = $811.83       $887.2493   $887.25   $887.25   $887.30