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 $151.57   8.504%   $164.4595   $164.46   $164.45   $164.50  
  Purchase #2 $167.61   8.747%   $182.2708   $182.27   $182.25   $182.30  
  Purchase #3 $101.93   6.536%   $108.5921   $108.59   $108.60   $108.60  
  Purchase #4 $72.54   6.777%   $77.456   $77.46   $77.45   $77.50  
  Purchase #5 $238.56   5.404%   $251.4518   $251.45   $251.45   $251.50  
  Purchase #6 $240.35   7.842%   $259.1982   $259.20   $259.20   $259.20  
  Purchase #7 $176.54   3.792%   $183.2344   $183.23   $183.25   $183.20  
  7 purchase totals = $1,149.10       $1,226.6628   $1,226.66   $1,226.65   $1,226.80