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 $204.84   8.182%   $221.6   $221.60   $221.60   $221.60  
  Purchase #2 $60.72   10.746%   $67.245   $67.25   $67.25   $67.20  
  Purchase #3 $13.84   8.331%   $14.993   $14.99   $15.00   $15.00  
  Purchase #4 $113.83   7.529%   $122.4003   $122.40   $122.40   $122.40  
  Purchase #5 $105.26   6.485%   $112.0861   $112.09   $112.10   $112.10  
  Purchase #6 $49.29   4.102%   $51.3119   $51.31   $51.30   $51.30  
  Purchase #7 $241.46   8.857%   $262.8461   $262.85   $262.85   $262.80  
  7 purchase totals = $789.24       $852.4824   $852.49   $852.50   $852.40