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	$248.47	3.485%	$257.1292	$257.13	$257.15	$257.10
Purchase #2	$56.66	4.682%	$59.3128	$59.31	$59.30	$59.30
Purchase #3	$72.78	13.853%	$82.8622	$82.86	$82.85	$82.90
Purchase #4	$55.65	10.602%	$61.55	$61.55	$61.55	$61.60
Purchase #5	$45.34	6.170%	$48.1375	$48.14	$48.15	$48.10
Purchase #6	$44.76	8.335%	$48.4907	$48.49	$48.50	$48.50
Purchase #7	$249.98	4.379%	$260.9266	$260.93	$260.95	$260.90
7 purchase totals =	$773.64		$818.4090	$818.41	$818.45	$818.40