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	$48.98	11.257%	$54.4937	$54.49	$54.50	$54.50
Purchase #2	$165.98	6.110%	$176.1214	$176.12	$176.10	$176.10
Purchase #3	$65.61	4.850%	$68.7921	$68.79	$68.80	$68.80
Purchase #4	$17.70	10.818%	$19.6148	$19.61	$19.60	$19.60
Purchase #5	$49.84	10.118%	$54.8828	$54.88	$54.90	$54.90
Purchase #6	$118.94	10.151%	$131.0136	$131.01	$131.00	$131.00
Purchase #7	$109.54	8.197%	$118.519	$118.52	$118.50	$118.50
7 purchase totals =	$576.59		$623.4374	$623.42	$623.40	$623.40