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 $115.59   3.181%   $119.2669   $119.27   $119.25   $119.30  
  Purchase #2 $163.34   11.691%   $182.4361   $182.44   $182.45   $182.40  
  Purchase #3 $201.93   4.396%   $210.8068   $210.81   $210.80   $210.80  
  Purchase #4 $43.88   5.175%   $46.1508   $46.15   $46.15   $46.20  
  Purchase #5 $60.44   7.801%   $65.1549   $65.15   $65.15   $65.20  
  Purchase #6 $167.67   9.736%   $183.9944   $183.99   $184.00   $184.00  
  Purchase #7 $43.57   13.669%   $49.5256   $49.53   $49.55   $49.50  
  7 purchase totals = $796.42       $857.3355   $857.34   $857.35   $857.40