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 $207.32   13.581%   $235.4761   $235.48   $235.50   $235.50  
  Purchase #2 $89.29   8.519%   $96.8966   $96.90   $96.90   $96.90  
  Purchase #3 $146.45   6.680%   $156.2329   $156.23   $156.25   $156.20  
  Purchase #4 $220.28   8.728%   $239.506   $239.51   $239.50   $239.50  
  Purchase #5 $87.50   9.815%   $96.0881   $96.09   $96.10   $96.10  
  Purchase #6 $243.63   3.426%   $251.9768   $251.98   $252.00   $252.00  
  Purchase #7 $20.35   3.300%   $21.0216   $21.02   $21.00   $21.00  
  7 purchase totals = $1,014.82       $1,097.1981   $1,097.21   $1,097.25   $1,097.20