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 $244.57   9.366%   $267.4764   $267.48   $267.50   $267.50  
  Purchase #2 $152.62   8.736%   $165.9529   $165.95   $165.95   $166.00  
  Purchase #3 $63.97   11.133%   $71.0918   $71.09   $71.10   $71.10  
  Purchase #4 $200.44   5.394%   $211.2517   $211.25   $211.25   $211.30  
  Purchase #5 $168.60   10.126%   $185.6724   $185.67   $185.65   $185.70  
  Purchase #6 $57.78   3.841%   $59.9993   $60.00   $60.00   $60.00  
  Purchase #7 $115.65   10.799%   $128.139   $128.14   $128.15   $128.10  
  7 purchase totals = $1,003.63       $1,089.5835   $1,089.58   $1,089.60   $1,089.70