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 $211.94   13.132%   $239.772   $239.77   $239.75   $239.80  
  Purchase #2 $36.36   3.426%   $37.6057   $37.61   $37.60   $37.60  
  Purchase #3 $118.95   9.763%   $130.5631   $130.56   $130.55   $130.60  
  Purchase #4 $81.55   5.396%   $85.9504   $85.95   $85.95   $86.00  
  Purchase #5 $129.91   7.390%   $139.5103   $139.51   $139.50   $139.50  
  Purchase #6 $224.61   7.468%   $241.3839   $241.38   $241.40   $241.40  
  Purchase #7 $173.75   5.313%   $182.9813   $182.98   $183.00   $183.00  
  7 purchase totals = $977.07       $1,057.7667   $1,057.76   $1,057.75   $1,057.90