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 $68.79   11.403%   $76.6341   $76.63   $76.65   $76.60  
  Purchase #2 $56.70   6.397%   $60.3271   $60.33   $60.35   $60.30  
  Purchase #3 $202.66   4.601%   $211.9844   $211.98   $212.00   $212.00  
  Purchase #4 $213.39   10.167%   $235.0854   $235.09   $235.10   $235.10  
  Purchase #5 $41.60   13.572%   $47.246   $47.25   $47.25   $47.20  
  Purchase #6 $50.30   11.388%   $56.0282   $56.03   $56.05   $56.00  
  Purchase #7 $209.37   4.232%   $218.2305   $218.23   $218.25   $218.20  
  7 purchase totals = $842.81       $905.5357   $905.54   $905.65   $905.40