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	$139.78	13.467%	$158.6042	$158.60	$158.60	$158.60
Purchase #2	$156.42	10.861%	$173.4088	$173.41	$173.40	$173.40
Purchase #3	$56.90	11.215%	$63.2813	$63.28	$63.30	$63.30
Purchase #4	$212.32	12.267%	$238.3653	$238.37	$238.35	$238.40
Purchase #5	$165.95	10.390%	$183.1922	$183.19	$183.20	$183.20
Purchase #6	$238.74	12.317%	$268.1456	$268.15	$268.15	$268.10
Purchase #7	$90.58	6.633%	$96.5882	$96.59	$96.60	$96.60
7 purchase totals =	$1,060.69		$1,181.5856	$1,181.59	$1,181.60	$1,181.60