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 $68.73   3.830%   $71.3624   $71.36   $71.35   $71.40  
  Purchase #2 $218.36   10.706%   $241.7376   $241.74   $241.75   $241.70  
  Purchase #3 $136.42   12.551%   $153.5421   $153.54   $153.55   $153.50  
  Purchase #4 $126.81   11.419%   $141.2904   $141.29   $141.30   $141.30  
  Purchase #5 $131.83   11.531%   $147.0313   $147.03   $147.05   $147.00  
  Purchase #6 $219.71   13.506%   $249.384   $249.38   $249.40   $249.40  
  Purchase #7 $241.25   11.202%   $268.2748   $268.27   $268.25   $268.30  
  7 purchase totals = $1,143.11       $1,272.6226   $1,272.61   $1,272.65   $1,272.60