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	$219.72	3.760%	$227.9815	$227.98	$228.00	$228.00
Purchase #2	$241.65	12.287%	$271.3415	$271.34	$271.35	$271.30
Purchase #3	$123.78	13.661%	$140.6896	$140.69	$140.70	$140.70
Purchase #4	$46.78	6.826%	$49.9732	$49.97	$49.95	$50.00
Purchase #5	$129.95	10.175%	$143.1724	$143.17	$143.15	$143.20
Purchase #6	$18.82	6.503%	$20.0439	$20.04	$20.05	$20.00
Purchase #7	$147.83	12.596%	$166.4507	$166.45	$166.45	$166.50
7 purchase totals =	$928.53		$1,019.6528	$1,019.64	$1,019.65	$1,019.70