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 $208.45   8.417%   $225.9952   $226.00   $226.00   $226.00  
  Purchase #2 $69.36   9.447%   $75.9124   $75.91   $75.90   $75.90  
  Purchase #3 $171.70   6.576%   $182.991   $182.99   $183.00   $183.00  
  Purchase #4 $16.44   13.556%   $18.6686   $18.67   $18.65   $18.70  
  Purchase #5 $124.73   8.235%   $135.0015   $135.00   $135.00   $135.00  
  Purchase #6 $55.25   6.268%   $58.7131   $58.71   $58.70   $58.70  
  Purchase #7 $68.87   8.790%   $74.9237   $74.92   $74.90   $74.90  
  7 purchase totals = $714.80       $772.2055   $772.20   $772.15   $772.20