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 $23.74   3.349%   $24.5351   $24.54   $24.55   $24.50  
  Purchase #2 $239.88   3.154%   $247.4458   $247.45   $247.45   $247.40  
  Purchase #3 $208.61   7.487%   $224.2286   $224.23   $224.25   $224.20  
  Purchase #4 $16.28   6.394%   $17.3209   $17.32   $17.30   $17.30  
  Purchase #5 $13.97   7.583%   $15.0293   $15.03   $15.05   $15.00  
  Purchase #6 $86.95   4.381%   $90.7593   $90.76   $90.75   $90.80  
  Purchase #7 $149.80   3.459%   $154.9816   $154.98   $155.00   $155.00  
  7 purchase totals = $739.23       $774.3006   $774.31   $774.35   $774.20