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 $68.71   11.462%   $76.5855   $76.59   $76.60   $76.60  
  Purchase #2 $98.40   9.134%   $107.3879   $107.39   $107.40   $107.40  
  Purchase #3 $45.70   12.391%   $51.3627   $51.36   $51.35   $51.40  
  Purchase #4 $214.64   5.511%   $226.4688   $226.47   $226.45   $226.50  
  Purchase #5 $94.58   3.567%   $97.9537   $97.95   $97.95   $98.00  
  Purchase #6 $183.73   4.122%   $191.3034   $191.30   $191.30   $191.30  
  Purchase #7 $154.69   13.170%   $175.0627   $175.06   $175.05   $175.10  
  7 purchase totals = $860.45       $926.1247   $926.12   $926.10   $926.30