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	$161.99	3.720%	$168.016	$168.02	$168.00	$168.00
Purchase #2	$84.52	6.144%	$89.7129	$89.71	$89.70	$89.70
Purchase #3	$17.35	12.376%	$19.4972	$19.50	$19.50	$19.50
Purchase #4	$212.54	5.216%	$223.6261	$223.63	$223.65	$223.60
Purchase #5	$70.67	12.215%	$79.3023	$79.30	$79.30	$79.30
Purchase #6	$145.40	4.232%	$151.5533	$151.55	$151.55	$151.60
Purchase #7	$94.25	9.366%	$103.0775	$103.08	$103.10	$103.10
7 purchase totals =	$786.72		$834.7853	$834.79	$834.80	$834.80