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 $54.75   13.840%   $62.3274   $62.33   $62.35   $62.30  
  Purchase #2 $220.71   4.530%   $230.7082   $230.71   $230.70   $230.70  
  Purchase #3 $26.82   3.482%   $27.7539   $27.75   $27.75   $27.80  
  Purchase #4 $222.26   3.407%   $229.8324   $229.83   $229.85   $229.80  
  Purchase #5 $249.81   5.624%   $263.8593   $263.86   $263.85   $263.90  
  Purchase #6 $134.98   13.798%   $153.6045   $153.60   $153.60   $153.60  
  Purchase #7 $15.82   4.527%   $16.5362   $16.54   $16.55   $16.50  
  7 purchase totals = $925.15       $984.6219   $984.62   $984.65   $984.60