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 $88.94   8.204%   $96.2366   $96.24   $96.25   $96.20  
  Purchase #2 $244.66   3.260%   $252.6359   $252.64   $252.65   $252.60  
  Purchase #3 $188.55   5.359%   $198.6544   $198.65   $198.65   $198.70  
  Purchase #4 $95.62   9.852%   $105.0405   $105.04   $105.05   $105.00  
  Purchase #5 $172.63   9.208%   $188.5258   $188.53   $188.55   $188.50  
  Purchase #6 $23.91   12.839%   $26.9798   $26.98   $27.00   $27.00  
  Purchase #7 $146.63   4.136%   $152.6946   $152.69   $152.70   $152.70  
  7 purchase totals = $960.94       $1,020.7676   $1,020.77   $1,020.85   $1,020.70