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	$28.66	5.837%	$30.3329	$30.33	$30.35	$30.30
Purchase #2	$136.42	4.434%	$142.4689	$142.47	$142.45	$142.50
Purchase #3	$128.26	10.358%	$141.5452	$141.55	$141.55	$141.50
Purchase #4	$99.83	8.250%	$108.066	$108.07	$108.05	$108.10
Purchase #5	$82.90	9.556%	$90.8219	$90.82	$90.80	$90.80
Purchase #6	$244.87	8.748%	$266.2912	$266.29	$266.30	$266.30
Purchase #7	$211.42	6.739%	$225.6676	$225.67	$225.65	$225.70
7 purchase totals =	$932.36		$1,005.1937	$1,005.20	$1,005.15	$1,005.20