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	$203.93	9.213%	$222.7181	$222.72	$222.70	$222.70
Purchase #2	$142.81	9.723%	$156.6954	$156.70	$156.70	$156.70
Purchase #3	$92.54	4.144%	$96.3749	$96.37	$96.35	$96.40
Purchase #4	$157.46	10.422%	$173.8705	$173.87	$173.85	$173.90
Purchase #5	$62.39	3.333%	$64.4695	$64.47	$64.45	$64.50
Purchase #6	$48.86	9.577%	$53.5393	$53.54	$53.55	$53.50
Purchase #7	$61.77	13.465%	$70.0873	$70.09	$70.10	$70.10
7 purchase totals =	$769.76		$837.7550	$837.76	$837.70	$837.80