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 $83.50   3.371%   $86.3148   $86.31   $86.30   $86.30  
  Purchase #2 $137.77   13.391%   $156.2188   $156.22   $156.20   $156.20  
  Purchase #3 $169.94   9.268%   $185.69   $185.69   $185.70   $185.70  
  Purchase #4 $250.55   10.340%   $276.4569   $276.46   $276.45   $276.50  
  Purchase #5 $153.75   11.624%   $171.6219   $171.62   $171.60   $171.60  
  Purchase #6 $35.67   8.228%   $38.6049   $38.60   $38.60   $38.60  
  Purchase #7 $23.99   11.725%   $26.8028   $26.80   $26.80   $26.80  
  7 purchase totals = $855.17       $941.7101   $941.70   $941.65   $941.70