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 $116.56   8.493%   $126.4594   $126.46   $126.45   $126.50  
  Purchase #2 $235.41   11.421%   $262.2962   $262.30   $262.30   $262.30  
  Purchase #3 $73.88   9.376%   $80.807   $80.81   $80.80   $80.80  
  Purchase #4 $124.56   9.831%   $136.8055   $136.81   $136.80   $136.80  
  Purchase #5 $24.55   7.778%   $26.4595   $26.46   $26.45   $26.50  
  Purchase #6 $160.83   7.362%   $172.6703   $172.67   $172.65   $172.70  
  Purchase #7 $19.95   5.832%   $21.1135   $21.11   $21.10   $21.10  
  7 purchase totals = $755.74       $826.6114   $826.62   $826.55   $826.70