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	$165.74	4.247%	$172.779	$172.78	$172.80	$172.80
Purchase #2	$248.69	12.762%	$280.4278	$280.43	$280.45	$280.40
Purchase #3	$40.43	8.817%	$43.9947	$43.99	$44.00	$44.00
Purchase #4	$139.42	13.823%	$158.692	$158.69	$158.70	$158.70
Purchase #5	$245.44	9.604%	$269.0121	$269.01	$269.00	$269.00
Purchase #6	$229.45	10.311%	$253.1086	$253.11	$253.10	$253.10
Purchase #7	$114.40	5.339%	$120.5078	$120.51	$120.50	$120.50
7 purchase totals =	$1,183.57		$1,298.5220	$1,298.52	$1,298.55	$1,298.50