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	$229.94	11.572%	$256.5487	$256.55	$256.55	$256.50
Purchase #2	$158.47	8.240%	$171.5279	$171.53	$171.55	$171.50
Purchase #3	$155.92	10.170%	$171.7771	$171.78	$171.80	$171.80
Purchase #4	$161.26	5.277%	$169.7697	$169.77	$169.75	$169.80
Purchase #5	$102.43	4.719%	$107.2637	$107.26	$107.25	$107.30
Purchase #6	$86.49	4.485%	$90.3691	$90.37	$90.35	$90.40
Purchase #7	$125.61	6.381%	$133.6252	$133.63	$133.65	$133.60
7 purchase totals =	$1,020.12		$1,100.8814	$1,100.89	$1,100.90	$1,100.90