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	$42.31	3.148%	$43.6419	$43.64	$43.65	$43.60
Purchase #2	$85.56	4.631%	$89.5223	$89.52	$89.50	$89.50
Purchase #3	$126.69	7.410%	$136.0777	$136.08	$136.10	$136.10
Purchase #4	$111.32	11.311%	$123.9114	$123.91	$123.90	$123.90
Purchase #5	$28.85	3.214%	$29.7772	$29.78	$29.80	$29.80
Purchase #6	$91.41	6.375%	$97.2374	$97.24	$97.25	$97.20
Purchase #7	$61.56	12.381%	$69.1817	$69.18	$69.20	$69.20
7 purchase totals =	$547.70		$589.3496	$589.35	$589.40	$589.30