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	$51.76	4.666%	$54.1751	$54.18	$54.20	$54.20
Purchase #2	$98.38	13.139%	$111.3061	$111.31	$111.30	$111.30
Purchase #3	$120.38	6.624%	$128.354	$128.35	$128.35	$128.40
Purchase #4	$25.85	10.827%	$28.6488	$28.65	$28.65	$28.60
Purchase #5	$219.76	10.149%	$242.0634	$242.06	$242.05	$242.10
Purchase #6	$10.80	10.141%	$11.8952	$11.90	$11.90	$11.90
Purchase #7	$9.79	4.504%	$10.2309	$10.23	$10.25	$10.20
7 purchase totals =	$536.72		$586.6735	$586.68	$586.70	$586.70