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	$28.26	4.356%	$29.491	$29.49	$29.50	$29.50
Purchase #2	$11.59	10.329%	$12.7871	$12.79	$12.80	$12.80
Purchase #3	$50.43	10.739%	$55.8457	$55.85	$55.85	$55.80
Purchase #4	$174.60	7.463%	$187.6304	$187.63	$187.65	$187.60
Purchase #5	$41.36	4.839%	$43.3614	$43.36	$43.35	$43.40
Purchase #6	$92.32	12.148%	$103.535	$103.54	$103.55	$103.50
Purchase #7	$127.77	4.692%	$133.765	$133.77	$133.75	$133.80
7 purchase totals =	$526.33		$566.4156	$566.43	$566.45	$566.40