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	$84.86	6.139%	$90.0696	$90.07	$90.05	$90.10
Purchase #2	$110.97	5.256%	$116.8026	$116.80	$116.80	$116.80
Purchase #3	$245.91	12.184%	$275.8717	$275.87	$275.85	$275.90
Purchase #4	$245.30	3.618%	$254.175	$254.18	$254.20	$254.20
Purchase #5	$205.93	4.482%	$215.1598	$215.16	$215.15	$215.20
Purchase #6	$130.38	9.202%	$142.3776	$142.38	$142.40	$142.40
Purchase #7	$180.39	5.560%	$190.4197	$190.42	$190.40	$190.40
7 purchase totals =	$1,203.74		$1,284.8760	$1,284.88	$1,284.85	$1,285.00