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	$52.72	13.572%	$59.8752	$59.88	$59.90	$59.90
Purchase #2	$179.74	3.639%	$186.2807	$186.28	$186.30	$186.30
Purchase #3	$81.98	12.678%	$92.3734	$92.37	$92.35	$92.40
Purchase #4	$76.82	4.697%	$80.4282	$80.43	$80.45	$80.40
Purchase #5	$11.40	9.855%	$12.5235	$12.52	$12.50	$12.50
Purchase #6	$209.33	10.160%	$230.5979	$230.60	$230.60	$230.60
Purchase #7	$223.90	5.330%	$235.8339	$235.83	$235.85	$235.80
7 purchase totals =	$835.89		$897.9128	$897.91	$897.95	$897.90