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	$133.51	3.720%	$138.4766	$138.48	$138.50	$138.50
Purchase #2	$165.76	13.105%	$187.4828	$187.48	$187.50	$187.50
Purchase #3	$94.78	11.688%	$105.8579	$105.86	$105.85	$105.90
Purchase #4	$35.26	10.831%	$39.079	$39.08	$39.10	$39.10
Purchase #5	$57.77	6.506%	$61.5285	$61.53	$61.55	$61.50
Purchase #6	$35.75	8.406%	$38.7551	$38.76	$38.75	$38.80
Purchase #7	$250.54	7.718%	$269.8767	$269.88	$269.90	$269.90
7 purchase totals =	$773.37		$841.0566	$841.07	$841.15	$841.20