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	$155.62	13.572%	$176.7407	$176.74	$176.75	$176.70
Purchase #2	$198.52	13.289%	$224.9013	$224.90	$224.90	$224.90
Purchase #3	$229.83	3.404%	$237.6534	$237.65	$237.65	$237.70
Purchase #4	$39.78	4.217%	$41.4575	$41.46	$41.45	$41.50
Purchase #5	$18.78	6.713%	$20.0407	$20.04	$20.05	$20.00
Purchase #6	$70.63	13.721%	$80.3211	$80.32	$80.30	$80.30
Purchase #7	$73.63	6.172%	$78.1744	$78.17	$78.15	$78.20
7 purchase totals =	$786.79		$859.2891	$859.28	$859.25	$859.30