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 $63.37   5.212%   $66.6728   $66.67   $66.65   $66.70  
  Purchase #2 $108.91   11.739%   $121.6949   $121.69   $121.70   $121.70  
  Purchase #3 $90.85   4.757%   $95.1717   $95.17   $95.15   $95.20  
  Purchase #4 $208.25   7.105%   $223.0462   $223.05   $223.05   $223.00  
  Purchase #5 $248.33   13.835%   $282.6865   $282.69   $282.70   $282.70  
  Purchase #6 $44.85   5.816%   $47.4585   $47.46   $47.45   $47.50  
  Purchase #7 $217.31   4.234%   $226.5109   $226.51   $226.50   $226.50  
  7 purchase totals = $981.87       $1,063.2415   $1,063.24   $1,063.20   $1,063.30