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 $237.25   13.362%   $268.9513   $268.95   $268.95   $269.00  
  Purchase #2 $64.99   5.312%   $68.4423   $68.44   $68.45   $68.40  
  Purchase #3 $121.29   12.812%   $136.8297   $136.83   $136.85   $136.80  
  Purchase #4 $229.59   3.284%   $237.1297   $237.13   $237.15   $237.10  
  Purchase #5 $81.92   13.721%   $93.1602   $93.16   $93.15   $93.20  
  Purchase #6 $213.99   7.324%   $229.6626   $229.66   $229.65   $229.70  
  Purchase #7 $33.96   4.179%   $35.3792   $35.38   $35.40   $35.40  
  7 purchase totals = $982.99       $1,069.5550   $1,069.55   $1,069.60   $1,069.60