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 $175.58   13.791%   $199.7942   $199.79   $199.80   $199.80  
  Purchase #2 $226.34   10.742%   $250.6534   $250.65   $250.65   $250.70  
  Purchase #3 $218.64   9.515%   $239.4436   $239.44   $239.45   $239.40  
  Purchase #4 $168.25   8.528%   $182.5984   $182.60   $182.60   $182.60  
  Purchase #5 $61.29   12.112%   $68.7134   $68.71   $68.70   $68.70  
  Purchase #6 $139.29   13.688%   $158.356   $158.36   $158.35   $158.40  
  Purchase #7 $69.88   8.801%   $76.0301   $76.03   $76.05   $76.00  
  7 purchase totals = $1,059.27       $1,175.5891   $1,175.58   $1,175.60   $1,175.60