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	$135.55	12.798%	$152.8977	$152.90	$152.90	$152.90
Purchase #2	$183.25	6.675%	$195.4819	$195.48	$195.50	$195.50
Purchase #3	$108.83	13.473%	$123.4927	$123.49	$123.50	$123.50
Purchase #4	$19.82	12.467%	$22.291	$22.29	$22.30	$22.30
Purchase #5	$238.64	7.201%	$255.8245	$255.82	$255.80	$255.80
Purchase #6	$6.27	3.853%	$6.5116	$6.51	$6.50	$6.50
Purchase #7	$198.87	6.361%	$211.5201	$211.52	$211.50	$211.50
7 purchase totals =	$891.23		$968.0195	$968.01	$968.00	$968.00