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 $70.58   9.246%   $77.1058   $77.11   $77.10   $77.10  
  Purchase #2 $109.81   8.836%   $119.5128   $119.51   $119.50   $119.50  
  Purchase #3 $202.90   8.138%   $219.412   $219.41   $219.40   $219.40  
  Purchase #4 $57.60   11.535%   $64.2442   $64.24   $64.25   $64.20  
  Purchase #5 $140.96   3.514%   $145.9133   $145.91   $145.90   $145.90  
  Purchase #6 $82.62   9.862%   $90.768   $90.77   $90.75   $90.80  
  Purchase #7 $9.68   9.736%   $10.6224   $10.62   $10.60   $10.60  
  7 purchase totals = $674.15       $727.5785   $727.57   $727.50   $727.50