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 $247.97   8.668%   $269.464   $269.46   $269.45   $269.50  
  Purchase #2 $213.38   4.359%   $222.6812   $222.68   $222.70   $222.70  
  Purchase #3 $95.69   10.533%   $105.769   $105.77   $105.75   $105.80  
  Purchase #4 $180.57   6.456%   $192.2276   $192.23   $192.25   $192.20  
  Purchase #5 $23.35   7.332%   $25.062   $25.06   $25.05   $25.10  
  Purchase #6 $101.98   11.813%   $114.0269   $114.03   $114.05   $114.00  
  Purchase #7 $6.28   8.180%   $6.7937   $6.79   $6.80   $6.80  
  7 purchase totals = $869.22       $936.0244   $936.02   $936.05   $936.10