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	13.558%	$250.9291	$250.93	$250.95	$250.90
Purchase #2	$107.32	11.807%	$119.9913	$119.99	$120.00	$120.00
Purchase #3	$169.62	12.211%	$190.3323	$190.33	$190.35	$190.30
Purchase #4	$186.29	11.576%	$207.8549	$207.85	$207.85	$207.90
Purchase #5	$223.76	3.509%	$231.6117	$231.61	$231.60	$231.60
Purchase #6	$145.86	13.385%	$165.3834	$165.38	$165.40	$165.40
Purchase #7	$79.75	13.243%	$90.3113	$90.31	$90.30	$90.30
7 purchase totals =	$1,133.57		$1,256.4140	$1,256.40	$1,256.45	$1,256.40