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	$93.87	7.140%	$100.5723	$100.57	$100.55	$100.60
Purchase #2	$123.70	10.671%	$136.9	$136.90	$136.90	$136.90
Purchase #3	$242.77	13.531%	$275.6192	$275.62	$275.60	$275.60
Purchase #4	$29.79	11.311%	$33.1595	$33.16	$33.15	$33.20
Purchase #5	$40.60	5.843%	$42.9723	$42.97	$42.95	$43.00
Purchase #6	$97.91	6.681%	$104.4514	$104.45	$104.45	$104.50
Purchase #7	$146.93	13.624%	$166.9477	$166.95	$166.95	$166.90
7 purchase totals =	$775.57		$860.6224	$860.62	$860.55	$860.70