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	$18.70	4.631%	$19.566	$19.57	$19.55	$19.60
Purchase #2	$150.77	9.326%	$164.8308	$164.83	$164.85	$164.80
Purchase #3	$200.83	9.267%	$219.4409	$219.44	$219.45	$219.40
Purchase #4	$167.76	7.540%	$180.4091	$180.41	$180.40	$180.40
Purchase #5	$173.43	6.729%	$185.1001	$185.10	$185.10	$185.10
Purchase #6	$115.96	3.810%	$120.3781	$120.38	$120.40	$120.40
Purchase #7	$18.98	9.567%	$20.7958	$20.80	$20.80	$20.80
7 purchase totals =	$846.43		$910.5208	$910.53	$910.55	$910.50