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	$18.42	11.478%	$20.5342	$20.53	$20.55	$20.50
Purchase #2	$177.50	4.521%	$185.5248	$185.52	$185.50	$185.50
Purchase #3	$238.49	4.316%	$248.7832	$248.78	$248.80	$248.80
Purchase #4	$93.84	4.252%	$97.8301	$97.83	$97.85	$97.80
Purchase #5	$7.33	5.179%	$7.7096	$7.71	$7.70	$7.70
Purchase #6	$7.33	3.564%	$7.5912	$7.59	$7.60	$7.60
Purchase #7	$11.48	11.112%	$12.7557	$12.76	$12.75	$12.80
7 purchase totals =	$554.39		$580.7288	$580.72	$580.75	$580.70