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	$84.45	11.675%	$94.3095	$94.31	$94.30	$94.30
Purchase #2	$83.43	7.543%	$89.7231	$89.72	$89.70	$89.70
Purchase #3	$101.98	8.855%	$111.0103	$111.01	$111.00	$111.00
Purchase #4	$118.81	10.866%	$131.7199	$131.72	$131.70	$131.70
Purchase #5	$44.88	8.404%	$48.6517	$48.65	$48.65	$48.70
Purchase #6	$200.65	9.564%	$219.8402	$219.84	$219.85	$219.80
Purchase #7	$114.26	12.142%	$128.1334	$128.13	$128.15	$128.10
7 purchase totals =	$748.46		$823.3881	$823.38	$823.35	$823.30