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	$217.82	6.701%	$232.4161	$232.42	$232.40	$232.40
Purchase #2	$38.78	8.522%	$42.0848	$42.08	$42.10	$42.10
Purchase #3	$125.56	8.864%	$136.6896	$136.69	$136.70	$136.70
Purchase #4	$100.58	8.669%	$109.2993	$109.30	$109.30	$109.30
Purchase #5	$175.91	5.665%	$185.8753	$185.88	$185.90	$185.90
Purchase #6	$132.32	10.280%	$145.9225	$145.92	$145.90	$145.90
Purchase #7	$16.95	13.705%	$19.273	$19.27	$19.25	$19.30
7 purchase totals =	$807.92		$871.5606	$871.56	$871.55	$871.60