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	$33.83	13.782%	$38.4925	$38.49	$38.50	$38.50
Purchase #2	$246.94	3.207%	$254.8594	$254.86	$254.85	$254.90
Purchase #3	$19.88	4.388%	$20.7523	$20.75	$20.75	$20.80
Purchase #4	$244.77	3.378%	$253.0383	$253.04	$253.05	$253.00
Purchase #5	$184.59	5.530%	$194.7978	$194.80	$194.80	$194.80
Purchase #6	$142.38	5.770%	$150.5953	$150.60	$150.60	$150.60
Purchase #7	$152.53	6.550%	$162.5207	$162.52	$162.50	$162.50
7 purchase totals =	$1,024.92		$1,075.0563	$1,075.06	$1,075.05	$1,075.10