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	$79.46	7.721%	$85.5951	$85.60	$85.60	$85.60
Purchase #2	$247.89	11.795%	$277.1286	$277.13	$277.15	$277.10
Purchase #3	$127.50	10.104%	$140.3826	$140.38	$140.40	$140.40
Purchase #4	$41.32	5.546%	$43.6116	$43.61	$43.60	$43.60
Purchase #5	$222.64	3.522%	$230.4814	$230.48	$230.50	$230.50
Purchase #6	$27.98	10.109%	$30.8085	$30.81	$30.80	$30.80
Purchase #7	$48.68	10.466%	$53.7748	$53.77	$53.75	$53.80
7 purchase totals =	$795.47		$861.7826	$861.78	$861.80	$861.80