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 $207.61   13.748%   $236.1522   $236.15   $236.15   $236.20  
  Purchase #2 $56.47   10.795%   $62.5659   $62.57   $62.55   $62.60  
  Purchase #3 $53.97   4.846%   $56.5854   $56.59   $56.60   $56.60  
  Purchase #4 $5.53   5.477%   $5.8329   $5.83   $5.85   $5.80  
  Purchase #5 $183.48   7.125%   $196.553   $196.55   $196.55   $196.60  
  Purchase #6 $187.63   6.521%   $199.8654   $199.87   $199.85   $199.90  
  Purchase #7 $147.58   9.288%   $161.2872   $161.29   $161.30   $161.30  
  7 purchase totals = $842.27       $918.8420   $918.85   $918.85   $919.00