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 $70.81   9.224%   $77.3415   $77.34   $77.35   $77.30  
  Purchase #2 $124.49   13.848%   $141.7294   $141.73   $141.75   $141.70  
  Purchase #3 $114.42   9.698%   $125.5165   $125.52   $125.50   $125.50  
  Purchase #4 $23.43   13.863%   $26.6781   $26.68   $26.70   $26.70  
  Purchase #5 $242.45   6.771%   $258.8663   $258.87   $258.85   $258.90  
  Purchase #6 $153.68   9.537%   $168.3365   $168.34   $168.35   $168.30  
  Purchase #7 $124.41   8.567%   $135.0682   $135.07   $135.05   $135.10  
  7 purchase totals = $853.69       $933.5365   $933.55   $933.55   $933.50