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	$158.53	7.296%	$170.0963	$170.10	$170.10	$170.10
Purchase #2	$89.62	9.656%	$98.2737	$98.27	$98.25	$98.30
Purchase #3	$241.64	12.698%	$272.3234	$272.32	$272.30	$272.30
Purchase #4	$245.30	4.176%	$255.5437	$255.54	$255.55	$255.50
Purchase #5	$192.98	9.597%	$211.5003	$211.50	$211.50	$211.50
Purchase #6	$114.86	3.521%	$118.9042	$118.90	$118.90	$118.90
Purchase #7	$226.29	12.811%	$255.28	$255.28	$255.30	$255.30
7 purchase totals =	$1,269.22		$1,381.9216	$1,381.91	$1,381.90	$1,381.90