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 $60.74   13.356%   $68.8524   $68.85   $68.85   $68.90  
  Purchase #2 $226.31   4.832%   $237.2453   $237.25   $237.25   $237.20  
  Purchase #3 $229.55   4.176%   $239.136   $239.14   $239.15   $239.10  
  Purchase #4 $63.76   13.805%   $72.5621   $72.56   $72.55   $72.60  
  Purchase #5 $59.92   11.462%   $66.788   $66.79   $66.80   $66.80  
  Purchase #6 $124.41   6.285%   $132.2292   $132.23   $132.25   $132.20  
  Purchase #7 $69.26   3.569%   $71.7319   $71.73   $71.75   $71.70  
  7 purchase totals = $833.95       $888.5449   $888.55   $888.60   $888.50