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 $58.85   13.194%   $66.6147   $66.61   $66.60   $66.60  
  Purchase #2 $163.70   11.573%   $182.645   $182.65   $182.65   $182.60  
  Purchase #3 $69.55   13.724%   $79.095   $79.10   $79.10   $79.10  
  Purchase #4 $131.45   10.416%   $145.1418   $145.14   $145.15   $145.10  
  Purchase #5 $90.55   7.668%   $97.4934   $97.49   $97.50   $97.50  
  Purchase #6 $200.90   3.330%   $207.59   $207.59   $207.60   $207.60  
  Purchase #7 $87.83   12.152%   $98.5031   $98.50   $98.50   $98.50  
  7 purchase totals = $802.83       $877.0830   $877.08   $877.10   $877.00