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 $127.55   12.665%   $143.7042   $143.70   $143.70   $143.70  
  Purchase #2 $43.83   6.771%   $46.7977   $46.80   $46.80   $46.80  
  Purchase #3 $131.78   3.779%   $136.76   $136.76   $136.75   $136.80  
  Purchase #4 $177.29   4.341%   $184.9862   $184.99   $185.00   $185.00  
  Purchase #5 $199.89   3.391%   $206.6683   $206.67   $206.65   $206.70  
  Purchase #6 $87.26   10.677%   $96.5768   $96.58   $96.60   $96.60  
  Purchase #7 $241.49   7.553%   $259.7297   $259.73   $259.75   $259.70  
  7 purchase totals = $1,009.09       $1,075.2229   $1,075.23   $1,075.25   $1,075.30