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	$121.37	12.125%	$136.0861	$136.09	$136.10	$136.10
Purchase #2	$209.25	8.443%	$226.917	$226.92	$226.90	$226.90
Purchase #3	$230.59	10.808%	$255.5122	$255.51	$255.50	$255.50
Purchase #4	$62.29	3.218%	$64.2945	$64.29	$64.30	$64.30
Purchase #5	$59.67	12.493%	$67.1246	$67.12	$67.10	$67.10
Purchase #6	$109.63	4.785%	$114.8758	$114.88	$114.90	$114.90
Purchase #7	$11.87	7.625%	$12.7751	$12.78	$12.80	$12.80
7 purchase totals =	$804.67		$877.5853	$877.59	$877.60	$877.60