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 $183.71   13.199%   $207.9579   $207.96   $207.95   $208.00  
  Purchase #2 $232.67   4.710%   $243.6288   $243.63   $243.65   $243.60  
  Purchase #3 $76.93   13.807%   $87.5517   $87.55   $87.55   $87.60  
  Purchase #4 $29.78   13.647%   $33.8441   $33.84   $33.85   $33.80  
  Purchase #5 $33.73   8.672%   $36.6551   $36.66   $36.65   $36.70  
  Purchase #6 $168.43   8.117%   $182.1015   $182.10   $182.10   $182.10  
  Purchase #7 $69.43   6.664%   $74.0568   $74.06   $74.05   $74.10  
  7 purchase totals = $794.68       $865.7959   $865.80   $865.80   $865.90