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 $126.51   10.420%   $139.6923   $139.69   $139.70   $139.70  
  Purchase #2 $191.97   7.511%   $206.3889   $206.39   $206.40   $206.40  
  Purchase #3 $158.94   11.525%   $177.2578   $177.26   $177.25   $177.30  
  Purchase #4 $127.25   4.154%   $132.536   $132.54   $132.55   $132.50  
  Purchase #5 $41.40   4.296%   $43.1785   $43.18   $43.20   $43.20  
  Purchase #6 $139.98   5.265%   $147.3499   $147.35   $147.35   $147.30  
  Purchase #7 $219.83   4.453%   $229.619   $229.62   $229.60   $229.60  
  7 purchase totals = $1,005.88       $1,076.0224   $1,076.03   $1,076.05   $1,076.00