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	$161.79	10.509%	$178.7925	$178.79	$178.80	$178.80
Purchase #2	$134.42	9.470%	$147.1496	$147.15	$147.15	$147.10
Purchase #3	$115.28	3.573%	$119.399	$119.40	$119.40	$119.40
Purchase #4	$84.97	3.432%	$87.8862	$87.89	$87.90	$87.90
Purchase #5	$81.79	10.139%	$90.0827	$90.08	$90.10	$90.10
Purchase #6	$66.89	6.213%	$71.0459	$71.05	$71.05	$71.00
Purchase #7	$33.78	13.732%	$38.4187	$38.42	$38.40	$38.40
7 purchase totals =	$678.92		$732.7746	$732.78	$732.80	$732.70