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 $240.38   5.247%   $252.9927   $252.99   $253.00   $253.00  
  Purchase #2 $155.68   6.549%   $165.8755   $165.88   $165.90   $165.90  
  Purchase #3 $248.78   11.737%   $277.9793   $277.98   $278.00   $278.00  
  Purchase #4 $65.58   9.297%   $71.677   $71.68   $71.70   $71.70  
  Purchase #5 $114.75   3.264%   $118.4954   $118.50   $118.50   $118.50  
  Purchase #6 $54.25   12.436%   $60.9965   $61.00   $61.00   $61.00  
  Purchase #7 $64.68   11.372%   $72.0354   $72.04   $72.05   $72.00  
  7 purchase totals = $944.10       $1,020.0518   $1,020.07   $1,020.15   $1,020.10