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	$11.73	3.705%	$12.1646	$12.16	$12.15	$12.20
Purchase #2	$236.83	6.203%	$251.5206	$251.52	$251.50	$251.50
Purchase #3	$54.50	9.826%	$59.8552	$59.86	$59.85	$59.90
Purchase #4	$164.58	8.731%	$178.9495	$178.95	$178.95	$178.90
Purchase #5	$92.50	8.860%	$100.6955	$100.70	$100.70	$100.70
Purchase #6	$193.44	9.494%	$211.8052	$211.81	$211.80	$211.80
Purchase #7	$133.69	6.538%	$142.4307	$142.43	$142.45	$142.40
7 purchase totals =	$887.27		$957.4213	$957.43	$957.40	$957.40