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 $167.68   6.762%   $179.0185   $179.02   $179.00   $179.00  
  Purchase #2 $226.34   8.508%   $245.597   $245.60   $245.60   $245.60  
  Purchase #3 $32.72   8.469%   $35.4911   $35.49   $35.50   $35.50  
  Purchase #4 $74.39   6.518%   $79.2387   $79.24   $79.25   $79.20  
  Purchase #5 $126.72   13.749%   $144.1427   $144.14   $144.15   $144.10  
  Purchase #6 $70.49   13.288%   $79.8567   $79.86   $79.85   $79.90  
  Purchase #7 $245.44   6.524%   $261.4525   $261.45   $261.45   $261.50  
  7 purchase totals = $943.78       $1,024.7972   $1,024.80   $1,024.80   $1,024.80