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	$182.35	6.160%	$193.5828	$193.58	$193.60	$193.60
Purchase #2	$111.71	5.536%	$117.8943	$117.89	$117.90	$117.90
Purchase #3	$67.85	12.125%	$76.0768	$76.08	$76.10	$76.10
Purchase #4	$38.92	10.536%	$43.0206	$43.02	$43.00	$43.00
Purchase #5	$25.64	13.559%	$29.1165	$29.12	$29.10	$29.10
Purchase #6	$73.51	11.734%	$82.1357	$82.14	$82.15	$82.10
Purchase #7	$94.60	4.663%	$99.0112	$99.01	$99.00	$99.00
7 purchase totals =	$594.58		$640.8379	$640.84	$640.85	$640.80