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 $55.45   11.218%   $61.6704   $61.67   $61.65   $61.70  
  Purchase #2 $231.75   6.387%   $246.5519   $246.55   $246.55   $246.60  
  Purchase #3 $23.78   11.777%   $26.5806   $26.58   $26.60   $26.60  
  Purchase #4 $187.52   3.335%   $193.7738   $193.77   $193.75   $193.80  
  Purchase #5 $46.28   10.683%   $51.2241   $51.22   $51.20   $51.20  
  Purchase #6 $134.35   4.813%   $140.8163   $140.82   $140.80   $140.80  
  Purchase #7 $56.64   11.423%   $63.11   $63.11   $63.10   $63.10  
  7 purchase totals = $735.77       $783.7271   $783.72   $783.65   $783.80