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	$84.75	6.702%	$90.4299	$90.43	$90.45	$90.40
Purchase #2	$89.32	4.293%	$93.1545	$93.15	$93.15	$93.20
Purchase #3	$232.58	8.179%	$251.6027	$251.60	$251.60	$251.60
Purchase #4	$127.50	4.178%	$132.827	$132.83	$132.85	$132.80
Purchase #5	$36.82	3.807%	$38.2217	$38.22	$38.20	$38.20
Purchase #6	$142.78	6.137%	$151.5424	$151.54	$151.55	$151.50
Purchase #7	$46.29	7.754%	$49.8793	$49.88	$49.90	$49.90
7 purchase totals =	$760.04		$807.6575	$807.65	$807.70	$807.60