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 $235.75   10.723%   $261.0295   $261.03   $261.05   $261.00  
  Purchase #2 $53.70   9.520%   $58.8122   $58.81   $58.80   $58.80  
  Purchase #3 $36.80   10.314%   $40.5956   $40.60   $40.60   $40.60  
  Purchase #4 $202.65   4.445%   $211.6578   $211.66   $211.65   $211.70  
  Purchase #5 $211.54   7.397%   $227.1876   $227.19   $227.20   $227.20  
  Purchase #6 $48.74   3.465%   $50.4288   $50.43   $50.45   $50.40  
  Purchase #7 $32.87   9.551%   $36.0094   $36.01   $36.00   $36.00  
  7 purchase totals = $822.05       $885.7209   $885.73   $885.75   $885.70