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	$9.64	10.205%	$10.6238	$10.62	$10.60	$10.60
Purchase #2	$28.74	8.295%	$31.124	$31.12	$31.10	$31.10
Purchase #3	$117.35	10.125%	$129.2317	$129.23	$129.25	$129.20
Purchase #4	$91.39	12.720%	$103.0148	$103.01	$103.00	$103.00
Purchase #5	$124.39	4.692%	$130.2264	$130.23	$130.25	$130.20
Purchase #6	$77.37	6.668%	$82.529	$82.53	$82.55	$82.50
Purchase #7	$59.62	13.579%	$67.7158	$67.72	$67.70	$67.70
7 purchase totals =	$508.50		$554.4655	$554.46	$554.45	$554.30