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 $76.43   12.424%   $85.9257   $85.93   $85.95   $85.90  
  Purchase #2 $236.51   9.798%   $259.6832   $259.68   $259.70   $259.70  
  Purchase #3 $192.28   8.458%   $208.543   $208.54   $208.55   $208.50  
  Purchase #4 $86.81   12.831%   $97.9486   $97.95   $97.95   $97.90  
  Purchase #5 $148.61   5.338%   $156.5428   $156.54   $156.55   $156.50  
  Purchase #6 $142.34   3.838%   $147.803   $147.80   $147.80   $147.80  
  Purchase #7 $69.86   6.254%   $74.229   $74.23   $74.25   $74.20  
  7 purchase totals = $952.84       $1,030.6753   $1,030.67   $1,030.75   $1,030.50