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 $180.39   8.564%   $195.8386   $195.84   $195.85   $195.80  
  Purchase #2 $249.78   4.756%   $261.6595   $261.66   $261.65   $261.70  
  Purchase #3 $185.95   5.777%   $196.6923   $196.69   $196.70   $196.70  
  Purchase #4 $232.36   12.116%   $260.5127   $260.51   $260.50   $260.50  
  Purchase #5 $70.78   5.235%   $74.4853   $74.49   $74.50   $74.50  
  Purchase #6 $169.58   6.511%   $180.6214   $180.62   $180.60   $180.60  
  Purchase #7 $115.51   10.720%   $127.8927   $127.89   $127.90   $127.90  
  7 purchase totals = $1,204.35       $1,297.7025   $1,297.70   $1,297.70   $1,297.70