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	$72.79	6.869%	$77.7899	$77.79	$77.80	$77.80
Purchase #2	$239.75	4.396%	$250.2894	$250.29	$250.30	$250.30
Purchase #3	$20.54	4.519%	$21.4682	$21.47	$21.45	$21.50
Purchase #4	$121.91	10.500%	$134.7106	$134.71	$134.70	$134.70
Purchase #5	$229.83	12.867%	$259.4022	$259.40	$259.40	$259.40
Purchase #6	$150.89	13.729%	$171.6057	$171.61	$171.60	$171.60
Purchase #7	$134.43	7.419%	$144.4034	$144.40	$144.40	$144.40
7 purchase totals =	$970.14		$1,059.6694	$1,059.67	$1,059.65	$1,059.70