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	$104.25	13.703%	$118.5354	$118.54	$118.55	$118.50
Purchase #2	$90.61	10.255%	$99.9021	$99.90	$99.90	$99.90
Purchase #3	$50.76	7.589%	$54.6122	$54.61	$54.60	$54.60
Purchase #4	$215.64	5.191%	$226.8339	$226.83	$226.85	$226.80
Purchase #5	$193.37	5.738%	$204.4656	$204.47	$204.45	$204.50
Purchase #6	$33.48	13.753%	$38.0845	$38.08	$38.10	$38.10
Purchase #7	$162.91	12.755%	$183.6892	$183.69	$183.70	$183.70
7 purchase totals =	$851.02		$926.1229	$926.12	$926.15	$926.10