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	$38.94	7.839%	$41.9925	$41.99	$42.00	$42.00
Purchase #2	$35.76	13.343%	$40.5315	$40.53	$40.55	$40.50
Purchase #3	$39.56	3.795%	$41.0613	$41.06	$41.05	$41.10
Purchase #4	$117.95	5.291%	$124.1907	$124.19	$124.20	$124.20
Purchase #5	$78.41	13.627%	$89.0949	$89.09	$89.10	$89.10
Purchase #6	$19.31	6.152%	$20.498	$20.50	$20.50	$20.50
Purchase #7	$203.97	12.376%	$229.2133	$229.21	$229.20	$229.20
7 purchase totals =	$533.90		$586.5822	$586.57	$586.60	$586.60