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	$74.76	5.479%	$78.8561	$78.86	$78.85	$78.90
Purchase #2	$31.97	7.281%	$34.2977	$34.30	$34.30	$34.30
Purchase #3	$237.86	8.373%	$257.776	$257.78	$257.80	$257.80
Purchase #4	$119.78	3.640%	$124.14	$124.14	$124.15	$124.10
Purchase #5	$17.77	13.342%	$20.1409	$20.14	$20.15	$20.10
Purchase #6	$248.80	9.204%	$271.6996	$271.70	$271.70	$271.70
Purchase #7	$121.83	4.690%	$127.5438	$127.54	$127.55	$127.50
7 purchase totals =	$852.77		$914.4541	$914.46	$914.50	$914.40