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	$126.72	12.708%	$142.8236	$142.82	$142.80	$142.80
Purchase #2	$149.82	12.202%	$168.101	$168.10	$168.10	$168.10
Purchase #3	$36.62	10.810%	$40.5786	$40.58	$40.60	$40.60
Purchase #4	$177.32	7.464%	$190.5552	$190.56	$190.55	$190.60
Purchase #5	$42.85	5.775%	$45.3246	$45.32	$45.30	$45.30
Purchase #6	$198.57	8.594%	$215.6351	$215.64	$215.65	$215.60
Purchase #7	$191.52	12.566%	$215.5864	$215.59	$215.60	$215.60
7 purchase totals =	$923.42		$1,018.6045	$1,018.61	$1,018.60	$1,018.60