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	$35.72	11.423%	$39.8003	$39.80	$39.80	$39.80
Purchase #2	$12.38	3.466%	$12.8091	$12.81	$12.80	$12.80
Purchase #3	$99.28	6.690%	$105.9218	$105.92	$105.90	$105.90
Purchase #4	$35.41	8.619%	$38.462	$38.46	$38.45	$38.50
Purchase #5	$171.92	5.323%	$181.0713	$181.07	$181.05	$181.10
Purchase #6	$61.58	12.538%	$69.3009	$69.30	$69.30	$69.30
Purchase #7	$180.30	6.517%	$192.0502	$192.05	$192.05	$192.10
7 purchase totals =	$596.59		$639.4156	$639.41	$639.35	$639.50