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	$122.43	7.766%	$131.9379	$131.94	$131.95	$131.90
Purchase #2	$46.29	4.521%	$48.3828	$48.38	$48.40	$48.40
Purchase #3	$172.88	11.517%	$192.7906	$192.79	$192.80	$192.80
Purchase #4	$47.38	6.707%	$50.5578	$50.56	$50.55	$50.60
Purchase #5	$158.93	4.642%	$166.3075	$166.31	$166.30	$166.30
Purchase #6	$7.40	5.704%	$7.8221	$7.82	$7.80	$7.80
Purchase #7	$63.64	8.550%	$69.0812	$69.08	$69.10	$69.10
7 purchase totals =	$618.95		$666.8799	$666.88	$666.90	$666.90