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	$109.35	6.247%	$116.1811	$116.18	$116.20	$116.20
Purchase #2	$118.61	7.515%	$127.5235	$127.52	$127.50	$127.50
Purchase #3	$186.34	3.279%	$192.4501	$192.45	$192.45	$192.50
Purchase #4	$191.88	10.841%	$212.6817	$212.68	$212.70	$212.70
Purchase #5	$19.35	3.831%	$20.0913	$20.09	$20.10	$20.10
Purchase #6	$126.50	10.637%	$139.9558	$139.96	$139.95	$140.00
Purchase #7	$102.42	7.816%	$110.4251	$110.43	$110.45	$110.40
7 purchase totals =	$854.45		$919.3086	$919.31	$919.35	$919.40