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	$74.92	6.215%	$79.5763	$79.58	$79.60	$79.60
Purchase #2	$100.86	10.157%	$111.1044	$111.10	$111.10	$111.10
Purchase #3	$203.65	10.610%	$225.2573	$225.26	$225.25	$225.30
Purchase #4	$128.47	10.827%	$142.3794	$142.38	$142.40	$142.40
Purchase #5	$128.75	6.335%	$136.9063	$136.91	$136.90	$136.90
Purchase #6	$17.55	4.365%	$18.3161	$18.32	$18.30	$18.30
Purchase #7	$63.64	13.297%	$72.1022	$72.10	$72.10	$72.10
7 purchase totals =	$717.84		$785.6420	$785.65	$785.65	$785.70