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	$69.30	13.559%	$78.6964	$78.70	$78.70	$78.70
Purchase #2	$170.78	5.792%	$180.6716	$180.67	$180.65	$180.70
Purchase #3	$175.72	12.736%	$198.0997	$198.10	$198.10	$198.10
Purchase #4	$90.45	12.255%	$101.5346	$101.53	$101.55	$101.50
Purchase #5	$139.74	12.113%	$156.6667	$156.67	$156.65	$156.70
Purchase #6	$39.46	12.605%	$44.4339	$44.43	$44.45	$44.40
Purchase #7	$58.67	13.778%	$66.7536	$66.75	$66.75	$66.80
7 purchase totals =	$744.12		$826.8565	$826.85	$826.85	$826.90