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	$99.64	9.666%	$109.2712	$109.27	$109.25	$109.30
Purchase #2	$111.94	12.575%	$126.0165	$126.02	$126.00	$126.00
Purchase #3	$244.63	12.774%	$275.879	$275.88	$275.90	$275.90
Purchase #4	$33.82	12.152%	$37.9298	$37.93	$37.95	$37.90
Purchase #5	$222.87	8.415%	$241.6245	$241.62	$241.60	$241.60
Purchase #6	$12.56	4.108%	$13.076	$13.08	$13.10	$13.10
Purchase #7	$112.74	5.411%	$118.8404	$118.84	$118.85	$118.80
7 purchase totals =	$838.20		$922.6374	$922.64	$922.65	$922.60