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	$184.37	13.620%	$209.4812	$209.48	$209.50	$209.50
Purchase #2	$104.53	13.192%	$118.3196	$118.32	$118.30	$118.30
Purchase #3	$92.64	5.645%	$97.8695	$97.87	$97.85	$97.90
Purchase #4	$61.58	4.358%	$64.2637	$64.26	$64.25	$64.30
Purchase #5	$120.47	6.534%	$128.3415	$128.34	$128.35	$128.30
Purchase #6	$10.52	4.493%	$10.9927	$10.99	$11.00	$11.00
Purchase #7	$57.49	3.265%	$59.367	$59.37	$59.35	$59.40
7 purchase totals =	$631.60		$688.6352	$688.63	$688.60	$688.70