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	$20.37	3.734%	$21.1306	$21.13	$21.15	$21.10
Purchase #2	$16.54	5.806%	$17.5003	$17.50	$17.50	$17.50
Purchase #3	$71.50	10.260%	$78.8359	$78.84	$78.85	$78.80
Purchase #4	$197.47	12.700%	$222.5487	$222.55	$222.55	$222.50
Purchase #5	$110.99	12.407%	$124.7605	$124.76	$124.75	$124.80
Purchase #6	$108.96	4.746%	$114.1312	$114.13	$114.15	$114.10
Purchase #7	$48.59	7.335%	$52.1541	$52.15	$52.15	$52.20
7 purchase totals =	$574.42		$631.0613	$631.06	$631.10	$631.00