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 $60.94   4.201%   $63.5001   $63.50   $63.50   $63.50  
  Purchase #2 $192.33   3.313%   $198.7019   $198.70   $198.70   $198.70  
  Purchase #3 $149.40   5.209%   $157.1822   $157.18   $157.20   $157.20  
  Purchase #4 $173.76   8.549%   $188.6147   $188.61   $188.60   $188.60  
  Purchase #5 $161.84   3.553%   $167.5902   $167.59   $167.60   $167.60  
  Purchase #6 $52.66   8.599%   $57.1882   $57.19   $57.20   $57.20  
  Purchase #7 $136.25   10.335%   $150.3314   $150.33   $150.35   $150.30  
  7 purchase totals = $927.18       $983.1087   $983.10   $983.15   $983.10