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 $234.82   13.177%   $265.7622   $265.76   $265.75   $265.80  
  Purchase #2 $176.28   4.257%   $183.7842   $183.78   $183.80   $183.80  
  Purchase #3 $152.64   10.635%   $168.8733   $168.87   $168.85   $168.90  
  Purchase #4 $92.35   4.247%   $96.2721   $96.27   $96.25   $96.30  
  Purchase #5 $54.27   11.666%   $60.6011   $60.60   $60.60   $60.60  
  Purchase #6 $108.55   4.747%   $113.7029   $113.70   $113.70   $113.70  
  Purchase #7 $139.60   5.633%   $147.4637   $147.46   $147.45   $147.50  
  7 purchase totals = $958.51       $1,036.4595   $1,036.44   $1,036.40   $1,036.60