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 $248.33   6.723%   $265.0252   $265.03   $265.05   $265.00  
  Purchase #2 $62.81   10.773%   $69.5765   $69.58   $69.60   $69.60  
  Purchase #3 $116.29   7.231%   $124.6989   $124.70   $124.70   $124.70  
  Purchase #4 $32.92   4.813%   $34.5044   $34.50   $34.50   $34.50  
  Purchase #5 $57.58   13.406%   $65.2992   $65.30   $65.30   $65.30  
  Purchase #6 $177.95   8.755%   $193.5295   $193.53   $193.55   $193.50  
  Purchase #7 $35.25   7.676%   $37.9558   $37.96   $37.95   $38.00  
  7 purchase totals = $731.13       $790.5895   $790.60   $790.65   $790.60