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	$220.97	4.599%	$231.1324	$231.13	$231.15	$231.10
Purchase #2	$127.62	10.684%	$141.2549	$141.25	$141.25	$141.30
Purchase #3	$81.53	9.104%	$88.9525	$88.95	$88.95	$89.00
Purchase #4	$211.92	5.253%	$223.0522	$223.05	$223.05	$223.10
Purchase #5	$127.91	13.256%	$144.8657	$144.87	$144.85	$144.90
Purchase #6	$97.46	5.164%	$102.4928	$102.49	$102.50	$102.50
Purchase #7	$185.94	3.305%	$192.0853	$192.09	$192.10	$192.10
7 purchase totals =	$1,053.35		$1,123.8358	$1,123.83	$1,123.85	$1,124.00