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	$100.69	10.724%	$111.488	$111.49	$111.50	$111.50
Purchase #2	$79.44	13.150%	$89.8864	$89.89	$89.90	$89.90
Purchase #3	$122.57	13.527%	$139.15	$139.15	$139.15	$139.20
Purchase #4	$45.92	13.391%	$52.0691	$52.07	$52.05	$52.10
Purchase #5	$22.98	3.188%	$23.7126	$23.71	$23.70	$23.70
Purchase #6	$7.61	11.406%	$8.478	$8.48	$8.50	$8.50
Purchase #7	$179.63	4.293%	$187.3415	$187.34	$187.35	$187.30
7 purchase totals =	$558.84		$612.1256	$612.13	$612.15	$612.20