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	$61.48	7.358%	$66.0037	$66.00	$66.00	$66.00
Purchase #2	$233.42	13.367%	$264.6213	$264.62	$264.60	$264.60
Purchase #3	$203.96	10.248%	$224.8618	$224.86	$224.85	$224.90
Purchase #4	$19.44	4.601%	$20.3344	$20.33	$20.35	$20.30
Purchase #5	$215.98	7.437%	$232.0424	$232.04	$232.05	$232.00
Purchase #6	$214.54	11.147%	$238.4548	$238.45	$238.45	$238.50
Purchase #7	$13.40	12.104%	$15.0219	$15.02	$15.00	$15.00
7 purchase totals =	$962.22		$1,061.3403	$1,061.32	$1,061.30	$1,061.30