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	$28.87	10.586%	$31.9262	$31.93	$31.95	$31.90
Purchase #2	$239.54	12.558%	$269.6214	$269.62	$269.60	$269.60
Purchase #3	$82.97	6.346%	$88.2353	$88.24	$88.25	$88.20
Purchase #4	$73.52	6.528%	$78.3194	$78.32	$78.30	$78.30
Purchase #5	$84.95	12.448%	$95.5246	$95.52	$95.50	$95.50
Purchase #6	$242.79	9.734%	$266.4232	$266.42	$266.40	$266.40
Purchase #7	$222.76	9.680%	$244.3232	$244.32	$244.30	$244.30
7 purchase totals =	$975.40		$1,074.3733	$1,074.37	$1,074.30	$1,074.20