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	$10.47	6.586%	$11.1596	$11.16	$11.15	$11.20
Purchase #2	$51.93	7.454%	$55.8009	$55.80	$55.80	$55.80
Purchase #3	$139.32	13.565%	$158.2188	$158.22	$158.20	$158.20
Purchase #4	$126.78	7.684%	$136.5218	$136.52	$136.50	$136.50
Purchase #5	$244.37	10.792%	$270.7424	$270.74	$270.75	$270.70
Purchase #6	$181.58	4.721%	$190.1524	$190.15	$190.15	$190.20
Purchase #7	$178.32	9.272%	$194.8538	$194.85	$194.85	$194.90
7 purchase totals =	$932.77		$1,017.4497	$1,017.44	$1,017.40	$1,017.50