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 $238.86   12.224%   $268.0582   $268.06   $268.05   $268.10  
  Purchase #2 $44.65   9.391%   $48.8431   $48.84   $48.85   $48.80  
  Purchase #3 $117.83   8.106%   $127.3813   $127.38   $127.40   $127.40  
  Purchase #4 $32.69   4.766%   $34.248   $34.25   $34.25   $34.20  
  Purchase #5 $107.45   4.298%   $112.0682   $112.07   $112.05   $112.10  
  Purchase #6 $51.81   13.525%   $58.8173   $58.82   $58.80   $58.80  
  Purchase #7 $183.63   7.483%   $197.371   $197.37   $197.35   $197.40  
  7 purchase totals = $776.92       $846.7871   $846.79   $846.75   $846.80