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	$85.46	12.862%	$96.4519	$96.45	$96.45	$96.50
Purchase #2	$92.25	8.420%	$100.0175	$100.02	$100.00	$100.00
Purchase #3	$175.97	4.770%	$184.3638	$184.36	$184.35	$184.40
Purchase #4	$246.82	13.245%	$279.5113	$279.51	$279.50	$279.50
Purchase #5	$120.78	10.352%	$133.2831	$133.28	$133.30	$133.30
Purchase #6	$51.51	7.611%	$55.4304	$55.43	$55.45	$55.40
Purchase #7	$103.67	12.693%	$116.8288	$116.83	$116.85	$116.80
7 purchase totals =	$876.46		$965.8868	$965.88	$965.90	$965.90