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	$39.46	10.668%	$43.6696	$43.67	$43.65	$43.70
Purchase #2	$179.72	7.400%	$193.0193	$193.02	$193.00	$193.00
Purchase #3	$22.55	4.436%	$23.5503	$23.55	$23.55	$23.60
Purchase #4	$173.75	12.159%	$194.8763	$194.88	$194.90	$194.90
Purchase #5	$109.98	12.115%	$123.3041	$123.30	$123.30	$123.30
Purchase #6	$165.66	4.724%	$173.4858	$173.49	$173.50	$173.50
Purchase #7	$82.83	8.185%	$89.6096	$89.61	$89.60	$89.60
7 purchase totals =	$773.95		$841.5150	$841.52	$841.50	$841.60