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 $49.35   6.598%   $52.6061   $52.61   $52.60   $52.60  
  Purchase #2 $205.28   8.411%   $222.5461   $222.55   $222.55   $222.50  
  Purchase #3 $239.28   11.416%   $266.5962   $266.60   $266.60   $266.60  
  Purchase #4 $166.55   6.708%   $177.7222   $177.72   $177.70   $177.70  
  Purchase #5 $146.89   8.768%   $159.7693   $159.77   $159.75   $159.80  
  Purchase #6 $170.49   13.230%   $193.0458   $193.05   $193.05   $193.00  
  Purchase #7 $163.25   10.512%   $180.4108   $180.41   $180.40   $180.40  
  7 purchase totals = $1,141.09       $1,252.6965   $1,252.71   $1,252.65   $1,252.60