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 $50.34   11.161%   $55.9584   $55.96   $55.95   $56.00  
  Purchase #2 $249.82   10.537%   $276.1435   $276.14   $276.15   $276.10  
  Purchase #3 $29.36   13.643%   $33.3656   $33.37   $33.35   $33.40  
  Purchase #4 $230.51   3.103%   $237.6627   $237.66   $237.65   $237.70  
  Purchase #5 $70.83   12.459%   $79.6547   $79.65   $79.65   $79.70  
  Purchase #6 $161.96   10.638%   $179.1893   $179.19   $179.20   $179.20  
  Purchase #7 $19.74   5.845%   $20.8938   $20.89   $20.90   $20.90  
  7 purchase totals = $812.56       $882.8680   $882.86   $882.85   $883.00