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	$34.76	12.391%	$39.0671	$39.07	$39.05	$39.10
Purchase #2	$238.90	6.478%	$254.3759	$254.38	$254.40	$254.40
Purchase #3	$239.89	5.289%	$252.5778	$252.58	$252.60	$252.60
Purchase #4	$157.54	4.423%	$164.508	$164.51	$164.50	$164.50
Purchase #5	$109.35	5.274%	$115.1171	$115.12	$115.10	$115.10
Purchase #6	$151.87	13.598%	$172.5213	$172.52	$172.50	$172.50
Purchase #7	$162.70	7.357%	$174.6698	$174.67	$174.65	$174.70
7 purchase totals =	$1,095.01		$1,172.8370	$1,172.85	$1,172.80	$1,172.90