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	$96.92	3.574%	$100.3839	$100.38	$100.40	$100.40
Purchase #2	$26.52	8.736%	$28.8368	$28.84	$28.85	$28.80
Purchase #3	$202.73	12.598%	$228.2699	$228.27	$228.25	$228.30
Purchase #4	$48.90	13.785%	$55.6409	$55.64	$55.65	$55.60
Purchase #5	$207.61	4.514%	$216.9815	$216.98	$217.00	$217.00
Purchase #6	$160.98	3.626%	$166.8171	$166.82	$166.80	$166.80
Purchase #7	$90.46	4.827%	$94.8265	$94.83	$94.85	$94.80
7 purchase totals =	$834.12		$891.7566	$891.76	$891.80	$891.70