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 $236.48   4.125%   $246.2348   $246.23   $246.25   $246.20  
  Purchase #2 $70.53   8.661%   $76.6386   $76.64   $76.65   $76.60  
  Purchase #3 $172.54   4.471%   $180.2543   $180.25   $180.25   $180.30  
  Purchase #4 $166.57   11.797%   $186.2203   $186.22   $186.20   $186.20  
  Purchase #5 $89.72   8.183%   $97.0618   $97.06   $97.05   $97.10  
  Purchase #6 $8.43   9.815%   $9.2574   $9.26   $9.25   $9.30  
  Purchase #7 $175.39   7.476%   $188.5022   $188.50   $188.50   $188.50  
  7 purchase totals = $919.66       $984.1694   $984.16   $984.15   $984.20