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	$51.59	11.444%	$57.494	$57.49	$57.50	$57.50
Purchase #2	$207.83	4.839%	$217.8869	$217.89	$217.90	$217.90
Purchase #3	$105.52	8.342%	$114.3225	$114.32	$114.30	$114.30
Purchase #4	$47.72	11.405%	$53.1625	$53.16	$53.15	$53.20
Purchase #5	$170.35	10.599%	$188.4054	$188.41	$188.40	$188.40
Purchase #6	$181.58	10.296%	$200.2755	$200.28	$200.30	$200.30
Purchase #7	$41.59	8.644%	$45.185	$45.19	$45.20	$45.20
7 purchase totals =	$806.18		$876.7318	$876.74	$876.75	$876.80