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 $93.73   4.640%   $98.0791   $98.08   $98.10   $98.10  
  Purchase #2 $188.27   13.643%   $213.9557   $213.96   $213.95   $214.00  
  Purchase #3 $61.75   8.551%   $67.0302   $67.03   $67.05   $67.00  
  Purchase #4 $74.51   9.127%   $81.3105   $81.31   $81.30   $81.30  
  Purchase #5 $250.36   8.337%   $271.2325   $271.23   $271.25   $271.20  
  Purchase #6 $78.98   4.156%   $82.2624   $82.26   $82.25   $82.30  
  Purchase #7 $189.31   9.543%   $207.3759   $207.38   $207.40   $207.40  
  7 purchase totals = $936.91       $1,021.2463   $1,021.25   $1,021.30   $1,021.30