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	$79.78	13.776%	$90.7705	$90.77	$90.75	$90.80
Purchase #2	$96.35	3.546%	$99.7666	$99.77	$99.75	$99.80
Purchase #3	$162.99	13.158%	$184.4362	$184.44	$184.45	$184.40
Purchase #4	$72.88	9.745%	$79.9822	$79.98	$80.00	$80.00
Purchase #5	$54.61	5.593%	$57.6643	$57.66	$57.65	$57.70
Purchase #6	$207.95	8.812%	$226.2746	$226.27	$226.25	$226.30
Purchase #7	$131.80	11.205%	$146.5682	$146.57	$146.55	$146.60
7 purchase totals =	$806.36		$885.4626	$885.46	$885.40	$885.60