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 $242.93   11.838%   $271.6881   $271.69   $271.70   $271.70  
  Purchase #2 $158.94   13.532%   $180.4478   $180.45   $180.45   $180.40  
  Purchase #3 $81.57   13.493%   $92.5762   $92.58   $92.60   $92.60  
  Purchase #4 $48.82   6.292%   $51.8918   $51.89   $51.90   $51.90  
  Purchase #5 $153.70   5.202%   $161.6955   $161.70   $161.70   $161.70  
  Purchase #6 $217.52   4.676%   $227.6912   $227.69   $227.70   $227.70  
  Purchase #7 $111.48   8.796%   $121.2858   $121.29   $121.30   $121.30  
  7 purchase totals = $1,014.96       $1,107.2764   $1,107.29   $1,107.35   $1,107.30