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 $115.96   9.116%   $126.5309   $126.53   $126.55   $126.50  
  Purchase #2 $23.73   10.805%   $26.294   $26.29   $26.30   $26.30  
  Purchase #3 $243.96   3.634%   $252.8255   $252.83   $252.85   $252.80  
  Purchase #4 $41.42   11.614%   $46.2305   $46.23   $46.25   $46.20  
  Purchase #5 $33.65   9.819%   $36.9541   $36.95   $36.95   $37.00  
  Purchase #6 $76.87   5.441%   $81.0525   $81.05   $81.05   $81.10  
  Purchase #7 $243.83   5.399%   $256.9944   $256.99   $257.00   $257.00  
  7 purchase totals = $779.42       $826.8819   $826.87   $826.95   $826.90