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 $126.26   10.673%   $139.7357   $139.74   $139.75   $139.70  
  Purchase #2 $134.31   5.664%   $141.9173   $141.92   $141.90   $141.90  
  Purchase #3 $224.49   6.709%   $239.551   $239.55   $239.55   $239.60  
  Purchase #4 $244.54   3.235%   $252.4509   $252.45   $252.45   $252.50  
  Purchase #5 $208.48   4.174%   $217.182   $217.18   $217.20   $217.20  
  Purchase #6 $87.48   13.771%   $99.5269   $99.53   $99.55   $99.50  
  Purchase #7 $170.42   4.369%   $177.8656   $177.87   $177.85   $177.90  
  7 purchase totals = $1,195.98       $1,268.2294   $1,268.24   $1,268.25   $1,268.30