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	$170.90	4.229%	$178.1274	$178.13	$178.15	$178.10
Purchase #2	$248.66	7.166%	$266.479	$266.48	$266.50	$266.50
Purchase #3	$52.28	4.314%	$54.5354	$54.54	$54.55	$54.50
Purchase #4	$212.97	11.792%	$238.0834	$238.08	$238.10	$238.10
Purchase #5	$54.91	8.612%	$59.6388	$59.64	$59.65	$59.60
Purchase #6	$126.97	13.451%	$144.0487	$144.05	$144.05	$144.00
Purchase #7	$161.79	5.446%	$170.6011	$170.60	$170.60	$170.60
7 purchase totals =	$1,028.48		$1,111.5138	$1,111.52	$1,111.60	$1,111.40