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 $250.37   6.621%   $266.947   $266.95   $266.95   $266.90  
  Purchase #2 $156.47   10.477%   $172.8634   $172.86   $172.85   $172.90  
  Purchase #3 $53.70   13.320%   $60.8528   $60.85   $60.85   $60.90  
  Purchase #4 $16.45   6.827%   $17.573   $17.57   $17.55   $17.60  
  Purchase #5 $33.70   9.116%   $36.7721   $36.77   $36.75   $36.80  
  Purchase #6 $88.46   10.705%   $97.9296   $97.93   $97.95   $97.90  
  Purchase #7 $187.82   11.184%   $208.8258   $208.83   $208.85   $208.80  
  7 purchase totals = $786.97       $861.7637   $861.76   $861.75   $861.80