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 $55.79   8.786%   $60.6917   $60.69   $60.70   $60.70  
  Purchase #2 $115.45   12.626%   $130.0267   $130.03   $130.05   $130.00  
  Purchase #3 $151.43   7.553%   $162.8675   $162.87   $162.85   $162.90  
  Purchase #4 $166.55   8.413%   $180.5619   $180.56   $180.55   $180.60  
  Purchase #5 $208.95   8.396%   $226.4934   $226.49   $226.50   $226.50  
  Purchase #6 $38.58   11.482%   $43.0098   $43.01   $43.00   $43.00  
  Purchase #7 $37.61   10.588%   $41.5921   $41.59   $41.60   $41.60  
  7 purchase totals = $774.36       $845.2431   $845.24   $845.25   $845.30