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	$78.65	13.249%	$89.0703	$89.07	$89.05	$89.10
Purchase #2	$115.77	12.314%	$130.0259	$130.03	$130.05	$130.00
Purchase #3	$215.97	7.277%	$231.6861	$231.69	$231.70	$231.70
Purchase #4	$100.51	10.584%	$111.148	$111.15	$111.15	$111.10
Purchase #5	$171.88	4.760%	$180.0615	$180.06	$180.05	$180.10
Purchase #6	$46.32	8.593%	$50.3003	$50.30	$50.30	$50.30
Purchase #7	$16.36	3.566%	$16.9434	$16.94	$16.95	$16.90
7 purchase totals =	$745.46		$809.2355	$809.24	$809.25	$809.20