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 $24.75   5.624%   $26.1419   $26.14   $26.15   $26.10  
  Purchase #2 $135.30   9.122%   $147.6421   $147.64   $147.65   $147.60  
  Purchase #3 $201.80   11.635%   $225.2794   $225.28   $225.30   $225.30  
  Purchase #4 $69.45   10.468%   $76.72   $76.72   $76.70   $76.70  
  Purchase #5 $186.81   3.753%   $193.821   $193.82   $193.80   $193.80  
  Purchase #6 $165.44   5.790%   $175.019   $175.02   $175.00   $175.00  
  Purchase #7 $130.54   9.682%   $143.1789   $143.18   $143.20   $143.20  
  7 purchase totals = $914.09       $987.8023   $987.80   $987.80   $987.70