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	$7.48	6.696%	$7.9809	$7.98	$8.00	$8.00
Purchase #2	$74.45	4.806%	$78.0281	$78.03	$78.05	$78.00
Purchase #3	$95.51	4.839%	$100.1317	$100.13	$100.15	$100.10
Purchase #4	$141.75	13.537%	$160.9387	$160.94	$160.95	$160.90
Purchase #5	$35.49	10.829%	$39.3332	$39.33	$39.35	$39.30
Purchase #6	$111.30	3.835%	$115.5684	$115.57	$115.55	$115.60
Purchase #7	$113.76	6.784%	$121.4775	$121.48	$121.50	$121.50
7 purchase totals =	$579.74		$623.4585	$623.46	$623.55	$623.40