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 $235.74   13.547%   $267.6757   $267.68   $267.70   $267.70  
  Purchase #2 $159.94   11.871%   $178.9265   $178.93   $178.95   $178.90  
  Purchase #3 $183.64   12.678%   $206.9219   $206.92   $206.90   $206.90  
  Purchase #4 $156.50   13.522%   $177.6619   $177.66   $177.65   $177.70  
  Purchase #5 $71.49   9.600%   $78.353   $78.35   $78.35   $78.40  
  Purchase #6 $228.28   9.730%   $250.4916   $250.49   $250.50   $250.50  
  Purchase #7 $159.45   5.536%   $168.2772   $168.28   $168.30   $168.30  
  7 purchase totals = $1,195.04       $1,328.3078   $1,328.31   $1,328.35   $1,328.40