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 $61.26   6.112%   $65.0042   $65.00   $65.00   $65.00  
  Purchase #2 $115.25   13.609%   $130.9344   $130.93   $130.95   $130.90  
  Purchase #3 $123.40   12.153%   $138.3968   $138.40   $138.40   $138.40  
  Purchase #4 $65.59   4.298%   $68.4091   $68.41   $68.40   $68.40  
  Purchase #5 $140.87   7.731%   $151.7607   $151.76   $151.75   $151.80  
  Purchase #6 $158.32   12.746%   $178.4995   $178.50   $178.50   $178.50  
  Purchase #7 $161.77   7.274%   $173.5371   $173.54   $173.55   $173.50  
  7 purchase totals = $826.46       $906.5418   $906.54   $906.55   $906.50