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	$61.78	10.669%	$68.3713	$68.37	$68.35	$68.40
Purchase #2	$101.77	9.755%	$111.6977	$111.70	$111.70	$111.70
Purchase #3	$233.30	10.296%	$257.3206	$257.32	$257.30	$257.30
Purchase #4	$59.88	13.180%	$67.7722	$67.77	$67.75	$67.80
Purchase #5	$131.88	12.809%	$148.7725	$148.77	$148.75	$148.80
Purchase #6	$10.87	3.440%	$11.2439	$11.24	$11.25	$11.20
Purchase #7	$45.80	3.543%	$47.4227	$47.42	$47.40	$47.40
7 purchase totals =	$645.28		$712.6009	$712.59	$712.50	$712.60