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	$41.51	5.254%	$43.6909	$43.69	$43.70	$43.70
Purchase #2	$214.94	5.236%	$226.1943	$226.19	$226.20	$226.20
Purchase #3	$69.48	4.419%	$72.5503	$72.55	$72.55	$72.60
Purchase #4	$55.77	6.478%	$59.3828	$59.38	$59.40	$59.40
Purchase #5	$90.63	10.661%	$100.2921	$100.29	$100.30	$100.30
Purchase #6	$50.37	13.679%	$57.2601	$57.26	$57.25	$57.30
Purchase #7	$75.47	5.651%	$79.7348	$79.73	$79.75	$79.70
7 purchase totals =	$598.17		$639.1053	$639.09	$639.15	$639.20