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 $190.32   5.821%   $201.3985   $201.40   $201.40   $201.40  
  Purchase #2 $228.36   4.724%   $239.1477   $239.15   $239.15   $239.10  
  Purchase #3 $206.52   13.246%   $233.8756   $233.88   $233.90   $233.90  
  Purchase #4 $155.46   3.325%   $160.629   $160.63   $160.65   $160.60  
  Purchase #5 $160.75   4.197%   $167.4967   $167.50   $167.50   $167.50  
  Purchase #6 $208.57   13.291%   $236.291   $236.29   $236.30   $236.30  
  Purchase #7 $39.91   8.479%   $43.294   $43.29   $43.30   $43.30  
  7 purchase totals = $1,189.89       $1,282.1325   $1,282.14   $1,282.20   $1,282.10