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	$127.36	9.537%	$139.5063	$139.51	$139.50	$139.50
Purchase #2	$148.43	4.381%	$154.9327	$154.93	$154.95	$154.90
Purchase #3	$35.45	5.182%	$37.287	$37.29	$37.30	$37.30
Purchase #4	$29.51	5.201%	$31.0448	$31.04	$31.05	$31.00
Purchase #5	$132.36	7.221%	$141.9177	$141.92	$141.90	$141.90
Purchase #6	$30.54	3.871%	$31.7222	$31.72	$31.70	$31.70
Purchase #7	$141.72	12.635%	$159.6263	$159.63	$159.65	$159.60
7 purchase totals =	$645.37		$696.0370	$696.04	$696.05	$695.90