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	$132.33	10.694%	$146.4814	$146.48	$146.50	$146.50
Purchase #2	$31.39	7.277%	$33.6743	$33.67	$33.65	$33.70
Purchase #3	$135.55	5.482%	$142.9809	$142.98	$143.00	$143.00
Purchase #4	$160.30	4.170%	$166.9845	$166.98	$167.00	$167.00
Purchase #5	$159.76	12.392%	$179.5575	$179.56	$179.55	$179.60
Purchase #6	$62.27	3.752%	$64.6064	$64.61	$64.60	$64.60
Purchase #7	$37.64	5.678%	$39.7772	$39.78	$39.80	$39.80
7 purchase totals =	$719.24		$774.0622	$774.06	$774.10	$774.20