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	$202.70	6.502%	$215.8796	$215.88	$215.90	$215.90
Purchase #2	$56.86	12.235%	$63.8168	$63.82	$63.80	$63.80
Purchase #3	$221.56	9.458%	$242.5151	$242.52	$242.50	$242.50
Purchase #4	$10.92	12.658%	$12.3023	$12.30	$12.30	$12.30
Purchase #5	$36.69	12.510%	$41.2799	$41.28	$41.30	$41.30
Purchase #6	$58.36	6.784%	$62.3191	$62.32	$62.30	$62.30
Purchase #7	$131.98	12.288%	$148.1977	$148.20	$148.20	$148.20
7 purchase totals =	$719.07		$786.3105	$786.32	$786.30	$786.30