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 $24.93   4.102%   $25.9526   $25.95   $25.95   $26.00  
  Purchase #2 $174.66   10.433%   $192.8823   $192.88   $192.90   $192.90  
  Purchase #3 $36.47   13.133%   $41.2596   $41.26   $41.25   $41.30  
  Purchase #4 $217.83   13.479%   $247.1913   $247.19   $247.20   $247.20  
  Purchase #5 $39.62   6.164%   $42.0622   $42.06   $42.05   $42.10  
  Purchase #6 $130.32   11.381%   $145.1517   $145.15   $145.15   $145.20  
  Purchase #7 $244.27   8.397%   $264.7814   $264.78   $264.80   $264.80  
  7 purchase totals = $868.10       $959.2811   $959.27   $959.30   $959.50