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 $56.49   5.417%   $59.5501   $59.55   $59.55   $59.60  
  Purchase #2 $68.34   3.750%   $70.9028   $70.90   $70.90   $70.90  
  Purchase #3 $53.34   3.510%   $55.2122   $55.21   $55.20   $55.20  
  Purchase #4 $109.64   8.172%   $118.5998   $118.60   $118.60   $118.60  
  Purchase #5 $221.66   11.423%   $246.9802   $246.98   $247.00   $247.00  
  Purchase #6 $225.26   3.772%   $233.7568   $233.76   $233.75   $233.80  
  Purchase #7 $250.91   4.247%   $261.5661   $261.57   $261.55   $261.60  
  7 purchase totals = $985.64       $1,046.5680   $1,046.57   $1,046.55   $1,046.70