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 $212.27   12.726%   $239.2835   $239.28   $239.30   $239.30  
  Purchase #2 $113.86   10.856%   $126.2206   $126.22   $126.20   $126.20  
  Purchase #3 $40.66   3.274%   $41.9912   $41.99   $42.00   $42.00  
  Purchase #4 $62.25   3.438%   $64.3902   $64.39   $64.40   $64.40  
  Purchase #5 $184.81   9.205%   $201.8218   $201.82   $201.80   $201.80  
  Purchase #6 $115.50   10.629%   $127.7765   $127.78   $127.80   $127.80  
  Purchase #7 $244.73   3.201%   $252.5638   $252.56   $252.55   $252.60  
  7 purchase totals = $974.08       $1,054.0476   $1,054.04   $1,054.05   $1,054.10