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 $248.76   4.400%   $259.7054   $259.71   $259.70   $259.70  
  Purchase #2 $250.28   10.261%   $275.9612   $275.96   $275.95   $276.00  
  Purchase #3 $165.36   11.128%   $183.7613   $183.76   $183.75   $183.80  
  Purchase #4 $50.36   8.850%   $54.8169   $54.82   $54.80   $54.80  
  Purchase #5 $178.51   7.591%   $192.0607   $192.06   $192.05   $192.10  
  Purchase #6 $62.60   8.594%   $67.9798   $67.98   $68.00   $68.00  
  Purchase #7 $222.25   5.772%   $235.0783   $235.08   $235.10   $235.10  
  7 purchase totals = $1,178.12       $1,269.3636   $1,269.37   $1,269.35   $1,269.50