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	$29.98	3.686%	$31.0851	$31.09	$31.10	$31.10
Purchase #2	$239.25	6.588%	$255.0118	$255.01	$255.00	$255.00
Purchase #3	$84.37	6.389%	$89.7604	$89.76	$89.75	$89.80
Purchase #4	$202.46	4.658%	$211.8906	$211.89	$211.90	$211.90
Purchase #5	$126.71	3.325%	$130.9231	$130.92	$130.90	$130.90
Purchase #6	$21.94	3.106%	$22.6215	$22.62	$22.60	$22.60
Purchase #7	$142.78	5.424%	$150.5244	$150.52	$150.50	$150.50
7 purchase totals =	$847.49		$891.8169	$891.81	$891.75	$891.80