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	$16.27	12.296%	$18.2706	$18.27	$18.25	$18.30
Purchase #2	$108.84	10.385%	$120.143	$120.14	$120.15	$120.10
Purchase #3	$161.59	5.861%	$171.0608	$171.06	$171.05	$171.10
Purchase #4	$190.42	3.242%	$196.5934	$196.59	$196.60	$196.60
Purchase #5	$214.78	6.592%	$228.9383	$228.94	$228.95	$228.90
Purchase #6	$100.49	5.290%	$105.8059	$105.81	$105.80	$105.80
Purchase #7	$92.82	7.193%	$99.4965	$99.50	$99.50	$99.50
7 purchase totals =	$885.21		$940.3085	$940.31	$940.30	$940.30