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 $64.76   13.705%   $73.6354   $73.64   $73.65   $73.60  
  Purchase #2 $236.44   12.778%   $266.6523   $266.65   $266.65   $266.70  
  Purchase #3 $18.72   11.242%   $20.8245   $20.82   $20.80   $20.80  
  Purchase #4 $76.42   3.636%   $79.1986   $79.20   $79.20   $79.20  
  Purchase #5 $33.94   10.831%   $37.616   $37.62   $37.60   $37.60  
  Purchase #6 $147.33   8.798%   $160.2921   $160.29   $160.30   $160.30  
  Purchase #7 $236.57   7.106%   $253.3807   $253.38   $253.40   $253.40  
  7 purchase totals = $814.18       $891.5996   $891.60   $891.60   $891.60